I also agree with the trainer. I am 15(almost 16) and have a friend who is 19/20. He started working out alittle later than me. But when he started we had the same bench. Now after a month(at most) his bench is like 60 pounds more than mine. Try changing your rountine to working each bodypart twice a week. I started doing that like a month ago and I am seeing much better strength and size gains.