In regards to you talking about adding 15 MPH to your fastball, that really isn't that hard if you were really dedicated and had a program you followed from a young age (middle/high school). I played baseball with a guy in HS when I was a Sophomore, the guy was a Junior, he probably consistently threw 65-72. In the offseason between Junior/Senior year he worked out everyday on a throwing program (long toss, weighted balls, lifting, throwing simulated games, etc) and his senior year he came out and was consistently throwing high 70's and could get it up into the mid 80's when he needed to. That was after less than 8 months of being on a throwing program, think if he had gotten more serious about conditioning his arm in say 7th/8th grade or even as a Freshman? He probably could have been throwing high 80's low 90's consistently by the time he was a senior.