I cannot understate how possible it is to throw 90 at 23. I mean it takes hard work and some genetic luck, but seriously how hard do you think the MLB pitcher who throws 90 now threw at 23?
EDIT: Now rereading your question, it'll take hard work but you could get your velocity back up. It'll be hard but it's possible. Get TUFFCUFF for starters. Also, you can play in independent/senior leagues that can help you get noticed, but not at 70 MPH.
Question: why'd you stop playing if you threw 90?!!?!?!??!?!