Good progress on the bench. What's the squat, deadlift and overhead press #'s? Is he cleaning yet? He's young so he's going to do "beach work". It isn't optimal, but anyone desiring style or appearance will. Just how it is, and I can talk until I'm blue in the face with a bunch of head nodding but convincing a kid he doesn't need to do it when his hormones are raging is usually a futile effort.
Really, I'd recommend using the Starting Strength linear progression model for him at this stage, at least for the next few months. It is the most effective / time efficient program to get strong, and doesn't cost a bunch of $$ if you have access to a squat rack and barbell. The main book would be
Basic Barbell Training (paperback version, although there is also a Kindle version if you have that app). This *really* emphasizes the technique on the lifts, far more than just about any other literature out there. The main programming book would be
Practical Programming for Strength Training (paperback version, although again there is a Kindle version if you have the app), but this isn't something you really need for a few months for your boy - it helps develop what the kid should do once he's exhausted his linear progression. Specifically for you, there's also
The Barbell Prescription (paperback version, again it is also on Kindle) which talks about programming and for those of us over 40, and why lifting is better for longevity than other more trendy endeavors.
Couple of things: From an exercise / lift standpoint, this program emphasizes utlilzing entire body movement weight training over anything targeting specific muscles, and the squat gets the most attention. If properly done, your boy won't have any issue gaining 20 lbs provided he continues to eat. He'll also no longer fit into any of his pants after about 3 months because his thighs / ass will grow, so beware. This specific program also (at least during linear progression) focuses on just doing the basic lifts and adding weight each time, which means it's best to completely cut the accessory stuff with flies, curls, etc. If the boy's concerned with his biceps, he can do chinups and eventually weighted chinups. Cleans are important, especially as the boy does football. He will notice a difference in his explosiveness even after just a few weeks, so those cannot be neglected.
There are hundreds, if not thousands, of different ways for your son to get bigger, stronger, and more ideal from a football perspective to be better on the field by utilizing weight training. And to be clear, I think this is the best way for you to get him there during the winter months. Once he's exhausted the linear progression, whether you want to utilize PPST, something from Barbell Medicine, Wendler... that's kinda up to your son (and you). But I would imagine at that point he'll be (rough numbers) benching 250, squatting 300+ and deadlifting 400. His performance on the field will be noticeably better.