I'm 40 and going for it. There are many mixed messages on the subject.
I am just completing my training and will have to build hours somehow to make my log book sexier.
I have had some people say that it will take me longer to train for a type rating but they'll like me more as I will be more likely to stay with an airline. Also a 55+ captain would rather have someone closer to their own age next to them than a 21 year old who they can't relate to.
One of the most negative people on the subject of age was the careers chap at Oxford.