I FIRE'd at 29. So yes, I thought of it in my 20s. As did MMM, I'm sure.
Like I've said before, your time to FIRE is merely a product of when you stumble on the idea and how much baggage (debt, lifestyle expenses, etc.) you have when you get do.
You all posting in this thread being in your 20s have a HUGE jump on most people. If you do it right, you can FIRE extremely early. Even if you do an okay job, you'll still FIRE by 50 or so, over a decade before the "normal" age.
It's best not to think about FIRE all the time though, IMO. Get yourself set up, save excess, and then live the life you want. Thinking about FIRE, past the point of optimization and motivation, doesn't help.
Good luck! :)