I also did personal bests for my 50/100 breast in my mid thirties. I stopped training at 18 and, while I occasionally played at it, only trained regularly from 34 on. I do 3 hours a week in the pool, and try to do the same on land. I'm 40 this year and wouldn't rule out doing more - it's not so much a physical challenge, but one of time and lifestyle. I'd love to get close again over 200 breast - probably don't do enough pool time to actually PB again, but hey ho - other things are important.