I knew plenty of athletes who juiced in college, but most often it didnt help as much as they thought because it was a head game...they onl worked hard when on, and were all bummed when off....at 21 your natural hormonal cocktail is better than a good cycle so you have all you need to work on your speed and power...
If you know how to train, eat, and supplement right, at your age you should be able to make huge improvements...
Juice will help you recover faster now, but in long run of your athletic career probably just lower your natural T levels if you end up doing it less than optimal...plus these days we know enough about recovery to do some amazing things, rolling out on hard rollerrs, tennis balls, LAX balls, doing lots of self myofascial release, using The Stick, ice baths, massage, various kinds of stretching, relaxation strategies post workout and before bed....with the right kinds of self care and supplementation you can improve recovery, hence training hard again on the track and in the weightroom
Do power cleans, snatches, squats, plyos...get a good strength coach, and if you dont have one already speed coach, work on your gains in the weightroom and in technique on the track, and someone who knows how to program both your weightroom and track workouts together to make the best gains....then find someone to help you with nutrition and supplements, of which this might not be the best place because athletic performance is a different world than bodybuilding all together....that goes for your training, diet, and supplements...youre going to be doing something different than most folks on here who are training for looks and my impression is most of us on here are way older than you...
If you are not already focus on learning the olympic lifts from a good coach, and improve whatever you can in your run technique, and get someone who can mastermind your workout strategy