Okay, fungo, I'll be more specific just for you.
Don't set unrealistic expectations based on what is happening at 14YO. I've seen kids lose velocity, as previously mentioned. I've seen others who were "early bloomers" and never gained any significant speed.
And yes, others continued to pick up velocity. I've seen 14YO's who were throwing 73 at 14YO reach 88 before they turned 17YO.
I have yet to see anyone reliably predict what speed a 14YO will be throwing when he hits 17 or 18YO. Thus it is unwise to set future expectations, IMHO.
At 14YO, velocity is not the most important thing, IMHO. It is nice. So long as the pitcher is still working on command of his fastballs and c/u. And working on learning pitch selection, strategy and mental toughness. And hopefully having some fun.
Perhaps this has added some clarity, at the expense of brevity.