Don't wait. Get an idea, get a co-founder and hit the ground running. Three years sounds like plenty of time, but it took me eight years and four failed attempts at the same goal to get where I wanted to go.
You can't count on having a perfect run. Experiment now while you still have more time on your hands.
I'm not sure where I'll be in three years, but it does help to have a direction. I am married and we do want kids around the same time so that would obviously complicate things, which is partly why I'm trying to figure this out now. Again, thanks for the comments.