My son was 5' and maybe 100 lbs when he started HS. He had touched 90 by the end of his junior year...at 5'9, maybe 145....and graduated at 5'11 and 155. Exit velo in the low 90's and sitting 88-89 even in the late innings. He's 6', 180 now and has been up to 93 in college. Size doesn't matter. Put in the work, get stronger and your son will be fine. 88 EV as a 14 year old is awfully good. 94 is ridiculously good. Don't worry about what other kids are doing...just have your son work hard and good things will happen.