I loved the WOW Jet Ski tour of Old San Juan. If you want an adrenaline filled adventure, while getting an interesting look at historical buildings, plus a short explanation of some of the history of El Morro, this is THE tour not to miss. You can jetski AND see Old San Juan like never before. You can have up to two per jetski (and the price is per jetski, not per person). The tour itself is a bit over an hour. Just ensure that you meet the guide at the correct spot…The same school exists in Isla Verde for Jet Ski rentals, but they do not do the Old San Juan tour (which I highly recommend the Old San Juan tour). The meeting point is close to the Isla Grande Airport near Sizzler restaurant.
If you want to Jet ski while in San Juan Puerto Rico, you will not be disappointed with WOW. Family owned and local business. They also offer a surf school, so check them out.