You are not too old, not even by a long shot. I left the regional world in my early 40's and made my final jump to WN shortly after that. I can tell you that even at a place like WN with slow retirements and a single fleet, there hasn't been a single day that I have wished to be back at the regional level. Sure, you can make a very nice career as a regional CA, and I am not trying to belittle it in any sort, but being at one of the big 4 is night and day a better experience.

You wouldn't have a hard time at any of them at your age.