My wife and I are seniors and wondered about youngish crowd, but totally loved the area. We used bus 30 at half price to go downtown even though we had a rental car...very convenient. Bus stop was right outside our building.
Getting places was a breeze. Didn't have to use interstate much either.
We didn't do touristy things like most, but did drive 101 to Oceanside, go to city if Julian which is 60 miles away, and took a sail boat ride from Sutter Island. Rent bikes from Surf Monkey...good shape and cheap.