Eight months is a great age to start. And initially they aren't really swim lessons so much as they are bonding sessions, since you'll be in the water with her. I started my middle daughter at that age. It was funny, because she hated it at first . . . cried the whole sesson for the first 3 weeks. But I wouldn't give up, and on the fourth lesson (which happended to be on Mother's Day) she didn't cry! From that point forward she was hooked! And to this day (she is now 9) she is very comfortable in and under the water. I wish I had done the same with my oldest daughter (now 13), who is OK in the water but definitely not as comfortable -- I didn't start her with lessons until she was 3-4 years old.
It is so much fun! And for working moms (which I am) there are many programs out there that offer dates to fit our life styles. Enjoy!!