Here is ten ideas of what you can do:

1.- Get a customer. For your app. Someone that will pay to use it, get their actual money in your hand. (That will show you how good the idea is)

2.- Describe to me what your app does in ONE SENTENCE. One that a 3 year old can understand

3.- Tell me what comes after "because" meaning... I must use your app because.... "......... .........."

4.- Speck it out in all details - Google how people have done it before. Do not miss on any of the steps

5.- Outsource the first page and get it done - Do not spend more than 100 dollars on this

6.- Document each step of the way in a blog

7.- Do a video of "what you thought would happen" and "what is actually happening" - every day

8.- Think of 10 other apps

9.- Repeat all previous steps for the 10 other apps

10.- Teach me how to answer the question you just asked from idea to full execution.... and charge for the course

Your age has nothing to do with it. I was already working at Apple when I was 15. Your age isn't a limiting factor. Your skills and drive are all that matter. I've answered hundreds of questions about best practices in mobile development here on Clarity. I would suggest you look through them and figure out what applies to you.

Build it.

Normally I'd say, "First check whether similar apps are already out there."

But who cares if you're replicating something that has already been marketed? You're 18! Nearly everything an undergrad will do at a university is redundant. We learn first of all by reproducing what's been done. So even if your app is "just another [fill in the blank]", you'll know how to run with your next newer idea. Anything you build looks good on a resume.

Prototype, build, ship, rince, repeat!
Wether you go iOS, Android, Web, that doesn't really matter, you don't need a designer to build a great app. All the tools are available there.
You don't need it to be perfect, just to be built.
If you idea is awesome, people will use it. The better the app, the more they'll use it, but for now, like Eric Ries would say, get out of the building!

If you are not a programmer, then put as much work as you can into sketching out and documenting how exactly you would envision or want this app to work.

Think about what a consumer or a person using the app would behave, and what he or she would want to do in the app. Put yourself in their shoes, and then write it out step by step. This is called use-case scenarios. Your app might have multiple use-cases. Think about ways your app users would use it that you might not have thought about.

Once you've written it down, make sure you also do the work of drawing or sketching each and every possible screen. If you have photoshop and know how to use it, consider buying a bootstrap app design from sites like ThemeForest (http://graphicriver.net/?ref=jmsierra). Do a search for bootstrap App UI. These can easily be modified to show/illustrate what your app would look like and how it would work at its most basic form.

Two final steps:

1) There are various tools available that allow you to create animated prototypes of an app. This means you can click through, and experience what the user might experience, without having to code (and of course, key technical functionality would not work). Use your sketches or photoshoped graphics to create a working prototype. This will allow you to test it and show it to potential users that can give you feedback.

2) Hire a programmer to code it for you. This is the harder and more expensive part. You can try to find a good app programmers viva websites like oDesk.com. The challenge here is that you need to vet and interview potential programmers as you would a new employee or hire. Assuming you don't have a lot of experience with that, it can be challenging (and expensive on the long run).

Or, if you know an app programmer in person, you can try to hire or contract out.

One last idea or suggestion -- once you have documented and sketched out your idea in detail, it could be a lot easier for you to potentially seek out a partner or investor willing to fund the development of your app. Before you take this path, you'll want to do some of the business research -- what are competing apps, are there other apps doing similar things, how much demand do you think there can be for your app, etc?

The main thing I would say to you right now -- continue fostering that creativity. Whether this app gets developed or not, sharpen those innovation skills by looking for problems around you and thinking about ways to solve them.

You don't need years of industry experience to create a killer app. What you DO need are
1. The idea
2. The ability to communicate the idea
3. The courage to share your idea to solicit and act-upon feedback from potential users/customers

You don't need to be a developer: There are plenty of great developers to whom you can outsource some/all of the development work if you wish.

You don't need to be a marketing whiz: Some simple strategies can massively improve the likelihood of getting your app noticed.

You don't need tons of cash: Most of your outlay will be in your own time and effort, and in the time and effort you require from others (e.g. developers, artists) to get your app built and modified during rapid iterations of honing your app, incorporating users' early feedback into improvements. You can use several techniques to reduce/eliminate the need to spend cash.

Here’s one of my own (fairly) recent app creation experiences:

In January 2012 I co-founded a startup with 3 other colleagues with a goal of building out some core platform offering services required by almost all game developers (e.g. authentication, licensing, scoring, achievements, etc.) Alas, we were ultimately unsuccessful in making that product work.

However, over lunch in July that year, with the US Presidential election looming, we had an idea:

Wouldn't it be fun to create an election-themed app that we could launch shortly before the election in order to test out at least some of the systems we'd built?

So we spent a couple of days white-boarding several ideas, honing down on the ideas that made us laugh the most. We chose 3 key ideas - two apps and an interactive video-based website.

All three would incorporate high-quality 3D models of the candidates: Barack Obama and Mitt Romey, in various activities. None of us were 3D artists so we outsourced the creation of the models of Obama and Romney.

The website would promote the apps and give a taste of our somewhat irreverent sense of humor: You'd choose the policies you thought were most important and depending on your choices, you'd see videos of the candidates fighting each other - the victor being the candidate most closely supporting the policies you selected. This was a blast to put together – choreographing the candidates’ moves made me feel like a martial-arts movie director :D

The first app, which took about 3 weeks to build, had either candidate performing one of three actions - boxing, dancing, walking flamboyantly, etc. We thought it was funny and quirky, but it only got downloaded a couple of hundred times a day - barely registering any interest at all in the iOS and Android app stores.

Deflated, we launched the 3rd app 3 weeks before the election: Gangnam President (https://www.youtube.com/watch?v=mi3gTWiGjDk) where we animated the candidates (and optional background dancers) dancing Gangnam Style in various locations including the Oval Office, in front of Air Force One, on the bridge of the Starship Enterprise, on the Great Wall of China, etc.

To our complete surprise, in its first day, Gangnam President was downloaded more than 50,000 times! It went on to be downloaded 1.5 million times in less than three weeks and became the #2 free iPad app of November 2012!

With no marketing, and only ~20 tweets/Facebook posts combined, Gangnam President took off with a life of its own.

Can lightning strike twice? At the end of November, we built another version of the app - Gangnam Santa. We replaced the candidates with a 3D model of Santa and replaced some of the background dancers with polar bears and penguins.

We launched the app 2 weeks before Xmas and ... it went nowhere. I think it got around 5000 total downloads over the Xmas period.

Success in trivial "fun" apps is neither guaranteed, nor is it lucrative ;) But it was enormous fun and we learned a TON about what it takes to build, launch, market, monetize and maintain apps in the app stores.

Let me know if you’d like to discuss further – I’ve a TON of hard-won experience (both technical as well as strategy) I can share with you to help you increase your odds of success :)

Work on converting your idea to reality, followed with further idea generation for monetization and/or value creation. And, while you do that, ensure to do it fast as you're young but your idea may not remain young for longer period of time. Otherwise, you can always use it this time to learn things around planning a business around an idea. All the best!!!

I am just a clarity away from further clarity!!