The sooner you get started, the better!
A big factor in REI, and investing in general, is time. The earlier you can get started, the bigger you can grow your investment. Time is definitely on our side (I'm 21 as well, bought my first SFR when I was 20 and recently added two more to my portfolio).
My best advice is to learn, learn, learn! Do your research! The idea of investing in property is a daunting task to tackle alone; but there are plenty of ways to gain experience/knowledge:
- BiggerPockets is a great source- it has thousands of threads, blog posts, and podcasts available to you for free.
- There are tons of great books out there on REI
- Look for a mentor! Reach out to family, friends, and others in your network to link up with someone who does the same thing you want to do. Take them to lunch, offer to do their grunt work, etc. A mentor can be an invaluable resource.
Do your research, crunch your numbers, and when an opportunity comes your way, don't be afraid to act on it!
Good luck!