The best gains for me were during my first year of lifting when I was 23 years old. I went from the mid-150lbs to close to 180 in a that year.
I was around 135lbs outta high school and after 4 years in the Marine Corps I had put on 20lbs without lifting weights just doing bodyweight exercises(pullups, pushups mainly with no lower body lifting, just military PT).
I lifted 3xweek that first year, push-pull-sometimes legs but usually armsLol! I worked out at a local small community college with a make-shift gym. It had a flat, incline, decline bench, and a jungle gym for all other body parts. There was one flimsy little squat rack that no one ever used as no one really worked legs. There was usually only 5-10 people working out at the most and we could only go on Mon-Wed-Thur because that was how the Continuing Ed. class was structured. I would try to copy whatever bodybuilder's routine was featured in that month"s Muscle and Fitness magazine(minus legs Lol!)
I only ate canned tuna, rice, and I did not eat a cheat meal for or any junk food because I thought that you could never cheat because that's how the "pros" said they ate in Muscle and Fitness Lol!
I took Weider Mega Mass, EAS creatine, HMB, Vanadyl Sulfate and a few other "hot" supplements at the time. The lady who led the class measured our body fat with a hand held caliper and she measured mine at 5.5% but I'm not sure how accurate she was. I was very lean and defined as I had always been very skinny throughout my life, but now I had a little muscle showing and was naturally vascular. One of my friends younger naive brother who was a teenager asked me if I was on steroids at a WHOPPING 175lbs Lol!
Those were the "good ol' days" when I could eat anything and grow and not get fat.