I'm guessing you know nothing about this and threw this out there? You'd be amazed what an athlete in his prime can do when their job is to eat correctly and work out and actually do it every single day for an extended period of time. Football players transitioning from high school ball to college ball do this all the time. If you're implying that they are taking something to add the muscle, I'd be curious to know what you believe it to be. They are actively screening for steroid use at this point (obviously) and despite the fact that everyone loves to point the finger at HGH, multiple studies have shown that HGH negligible benefits to athletes. It would be harder for an athlete in their prime to gain 20 pounds of muscle- harder than pretty much anyone else in the world. If they've peaked already than yes. My guess is 6'4 DJ LeMahieu never really pushed himself too much on gaining weight if he was only ever 180 lbs. My point was more of the fact that a 23 year old male can take on a brutal weight lifting regimen and potentially gain 19 lbs of muscle over the course of 4 or 5 months. At least more capably than a 48 year old female. Yes, he'd typically be more capable of adding muscle than an older female, but he still wouldn't be able to add 19 pounds of muscle in 4-5 months. A guy could probably add that much in a year, provided they'd never lifted weights before, or only did so poorly. To clarify my position, please remember I'm talking about muscle gain. People can certainly gain body weight at a much faster clip than they gain muscle weight. 20 pounds of muscle in three months is pretty much impossible without the benefit of puberty, or maybe steroids.