I had a couple of stays when I was 15-17 around my birthday with a friend, though I did not have an account at the time, so I don't necessarily count it. My first Hyatt stay, by myself, was sophomore year of college. I stayed at the Hyatt Place MCI the night before I did a mileage run to MSY on UAL. Just prior to my trip, I joined Gold Passport and requested a status match to Platinum

The only memorable, first stay, was at the HR SFO before doing a mileage run to TPA on UAL. I loved that property and had to have spent at least 25-40 nights with them throughout the remainder of college. The good old days of 744s flying SFO-ORD and cheap flights with plentiful upgrades.
I know I had previous stays with family, though it was on their account before I found FT and began earning my own points.
HP MCI
HR SFO