Let me say in a different way what AdelaaR perhaps meant: you did just fine for a first long ride, but at your age and weight if you want to, if you work at it, you will do a lot better before too long and have a lot of fun doing it! I, for one, won't be able to keep up with you for long.

In my experience your butt will adapt to the load and in a few weeks the soreness will pass even as the length of the rides increase. There are plenty of things you can do or buy to help, it is just that in my experience the butt needs no help, it just needs to be challenged to harden up.

Ken