Description
I rented my bike from San Juan bike rentals. They'll drop the bike off at your accommodation and come pick it up but you have to reserve it a day in advance. I don't think they have a storefront you can visit to pick up a bike.
My route https://ridewithgps.com/routes/49733422
Do not drive a car in Old San Juan. You'll see why.
Also there is nowhere to park. Only residents can park on the street.