Suppose you were to report for work, oh... one and half days (1.5) out of a five day workweek. How long do you think the paychecks would keep on coming. Or, suppose you were to report to class in school ... any school, with the same attendance record.
The answer to the above is obvious, of course - not good.
But, in the game of baseball this same equation - one and a half days out of five, or 30% is consider pretty darn good when we substitute days in attendance for pitcher Vs. batter stat. In baseball we just add another zero to the product = 300%.
I can overemphasize the importance for pitching strikes. Sure, a lot goes into the work, no debate there. But, that's what your job is - to pitch, not throw.
So, with all your questions about "how fast," .... "what's the velocity for my age," .... and so on, remember that strikes will always work in your favor. But, does this mean that you won't get hit, and hit badly in some games - of course not. On the other hand, your consistency to deliver a strike, one after the other, as a routine will soon develop into your ability to locate that strike to your advantage and that advantage that seven (7) other players behind you can provide.
While considering this topic here, don't fool yourself by giving examples of MLB play. You're an amateur at a level that doesn't even come close to MLB competition. You face an entirely different batting order and their abilities, your playing surface is "if-ee" at best, you don't have the opportunity to devote your life to training and conditioning yourself for this game for a living, and so on.