When I was 22 I got a job as a towel boy in a gym and one of the perks was a free membership. So I started asking all the trainers what to do and what to eat. They all said the same thing. Lift heavy and eat a lot. I was lifting like a pro and eating almost 6000 calories a day. Still no weight. At one point I switched to chicken thighs, rice, and steamed veggies 6 times a day and I LOST weight.
I'm 30 something now and a comfortable 167 lbs at around 12% body fat. I finally cracked the code and I feel like an idiot for not figuring it out sooner. I was eating more food than the rest of my family combined, but I was still extremely active. My metabolism was through the roof. I went back to eating whatever I wanted, but reduced my physical activities. I realized that it doesn't matter how much you eat if you're still extremely active. If you eat a lot and cant gain weight, then you need to reduce your physical activities throughout the day. I'm eating the same amount of food, but I cut my workouts down drastically, and I even make it a point to lounge around during the day. I'm still building muscle but I try to only do one exercise per body part, and pre-exhaust the muscle before each heavier set. I also don't lift as heavy as I used to.
I start with a pre-exhaustion set, usually with bands or cables to get blood into the muscle, then go straight into a working set with free weights for a total of 4-5 sets. In doing so, Im still stressing the muscle enough to make it grow, but keeping the workout short in order to keep from burning too many calories. And so far I've gained almost 30 lbs just in the last 2 months. So Lee Priest was right. Its not rocket science. Just eat food and train. But remember, if you're eating a ton of food and not gaining weight, slow down and try not to burn as much energy throughout the day. That's what worked for me, and hopefully it'll work for you.
