OK, I hate to write this stuff, but I am a genetic freak. In my adult life, it's never mattered if I do or do not workout, if I eat crappy or eat clean, I've stayed roughly the same weight for probably the last 15 years and I hate it. I wish I was huge like Arnold, but alas genetics failed me.
When I was heavy into weight lifting while in my mid-late 20s, my body would get stronger, but muscles would never get much larger. Depending on the training cycle I was on at the time, I'd be lifting anywhere between 3-6 days per week, with only mild cardio done for my heart health. I was taking Creatine and sometimes the Testosterone Booster (Weider made it I think?) as well as eating 4-5 meals per day and a weight gainer shake before bed. I did this for about 6 years straight and during this time my body weight flexed between 132-136 pounds (at 6 feet tall) and stayed in that range all those years. My metabolism is crazy fast.
I also spent about 4 years eating fast food a minimum of 5 days per week (usually 6 or 7, sometimes for two of my meals per day) and my weight still stayed between 132-136. I even had my cholesterol test at the doctors during this time and I'll never forget when he read my the blood test results. He said "It's pretty much unheard of for peoples cholesterol to be below 100. Yours is 88. You could basically eat sticks of butter and not have to worry about getting heart disease". He didn't realize I was already eating fast food almost every day of every month.
My body was so used to fast food as fuel during that time, whenever I tried to get on a healty diet, that's when I would get sick. Upper respitory infections, "head colds", stuff like that. I was in my late 20s at the time.
Eventually I switched jobs and was making less money so couldn't afford to eat out everyday so now eat a lot cleaner than I used to, but my weight is still in that same 132-136 range.
The heaviest weight I ever got in my life was in the year following my lung surgery. The surgeon just wanted me to eat, eat, eat to use the protein to repair the surgery. Since I was out of work for 3 months and literally sitting on my butt (not burning as much calories) and eating a lot, I got up to 148 pounds at my highest ever. But then I started working again and within the first year back to actually moving around again, I lost 20 pounds and ended that first 12 months back at 128. I did almost zero working out during that time. That's just from me going from months of inactivity back to normal job activity. Refer back to top to the "genetic freak" bits.
I do all the right stuff in the male prime age for working out (20s): Weight stays the same.
I eat like total crap for years straight: Weight stays the same.
I have my body weight go from 148 to 128 in one year without exercise, just going from inactivity after surgery back to normal work.
I've always been super skinny, but always dreamed to be muscley. People would always talk how my metabolism will slow down after I turn 'X' age, and they keep bumping it back every year.
Right now as I type this I'm still 132 pounds at age 37. I weighed myself on high school graduation day and I was 112, so at least I weigh 20 pounds more than I did back then. I turn 38 next month. Maybe THAT's the year my metabolism will start to slow down......