I'm in my 20s — is it too late to start?

Your 20s are literally the best time to start investing. You have 35-40 years of compounding ahead of you — that's where the real magic happens. Someone who starts investing $300/month at 25 will have more at 65 than someone who starts investing $600/month at 35. Time is your biggest advantage, and you have more of it than almost anyone. Start with whatever you can afford today.