Is it acceptable to wear kit from old team?
I guess it's a matter of opinion, and cyclists have a lot of rules, but personally I would go for it. You were actually on the team after all. I think that the rule #17 from the above link applies here. Personally, I'd rather wear old kit from a team I was personally on than wear kit from a pro team that I have no affiliation with, or even non-pro-kit with logos plastered all over it.  

Might even be a great way to start up a conversation with people who recognize the kit, either riders who are currently on the team or even just people who went to that school.