Sorry, my original post was geared a little too much toward things you're already working on---which I think is not actually what the YC 120 call is asking for. I think they're looking more for what you'd like to work on, and to the extent that you're doing anything now it's more about demonstrating potential.
In my opinion, if you've done work with a lot of different companies, that's actually great experience to have as a college student! Working is one of the best ways to get exposure to different sorts of problems and ways of approaching solutions.
Personally, the way I find problems to solve is by trying to do everyday sorts of things---be that building an app, game, a scientific simulation, a data analysis script or whatever---and then observing what's hard about it. Do this a couple times and you may start to see recurring problems. Usually my biggest problem is that I tend to undersell myself because these issues seem "obvious" to me after I've been in the trenches for a while. But sometimes the obvious problems are the most fundamental.
Anyway, if you have ideas of your own, I'd say just go for it. The instructions say they're "adjust[ing] for whatever life circumstances you were born into", and I think it's probably not unreasonable to expect them to adjust for e.g. age and stage of life as well. Compared to people in similar age categories I think you'll compare favorably in an application like this.
In my opinion, if you've done work with a lot of different companies, that's actually great experience to have as a college student! Working is one of the best ways to get exposure to different sorts of problems and ways of approaching solutions.
Personally, the way I find problems to solve is by trying to do everyday sorts of things---be that building an app, game, a scientific simulation, a data analysis script or whatever---and then observing what's hard about it. Do this a couple times and you may start to see recurring problems. Usually my biggest problem is that I tend to undersell myself because these issues seem "obvious" to me after I've been in the trenches for a while. But sometimes the obvious problems are the most fundamental.
Anyway, if you have ideas of your own, I'd say just go for it. The instructions say they're "adjust[ing] for whatever life circumstances you were born into", and I think it's probably not unreasonable to expect them to adjust for e.g. age and stage of life as well. Compared to people in similar age categories I think you'll compare favorably in an application like this.