Maybe. But it is a race against time, because once you get past 25 or so it will probably be much harder to improve.
It takes dedication though. Serious dedication. You have to be willing to make chess one of your life's top priorities, playing in tournaments almost every weekend, practicing and playing for hours every day, and analyzing your games to death. Coaching from at least a master level player will also help and may be a requirement at the higher levels.
The steps above took me from 962 U.S.C.F. to 1839 U.S.C.F. in about 19 months. However, it was easier for me than it will be for you because I am younger (16 years old). There is the possibility that you may have an innate talent for the game which could come out in the next year or two. But it will still take an enormous amount of work to reach FM. At 21 though it may well still be possible. Just extremely hard. The odds are stacked against you.
I'm 21 and I started playing last july. Here's my ratings.
Standard 1068 but I'm really lazy at standard online chess, last week I was 1180
Tactics 1048 (when I started playing was something about 700)
Chesstempo blitz 1278.5
Chesstempo standard 1186.8
The only thing I have to do is go to the University. I have no intention of having a girlfriend or kids so maybe I get more free time than a regular guy.