I have read that between 8-11 months is a bad time to sleep train because of separation anxiety and the natural sleep regression that happen around 9 months, but we are trying anyway.
The book i am reading about it is Healthy Sleep Habits, Happy Child, and it says that it is never too late to try to fix unhealthy sleep habits. it also gives different methods to try based on your comfort level ("no-cry", "some-cry", "cry-it-out"). It also gives methods for nap training as well.
We are only on day 2 of training but so far it hasn't been as bad as I expected.