Before making any steps to apply, you will both need to understand the lifestyle changes that are involved. Throughout training and into a career as a pilot, long days and unsociable hours are normal and it will impact both of you. You must both be happy with that. If you have children, how will it impact them? Some research and and understanding of this is required. If it's not workable for you, that's fine. It's a very different pace of life to working a 9-5 job!
Age isn't an issue here... Plenty of people in their 30's, and some older make a career change to the flight deck.
As long as you are both happy to make the change, the next thing is don't pin all of your hopes on the BA Speedbird Academy. I believe 10-20k people apply every time and it's hugely competitive. I think there are only around 100 places open, so we're looking at 0.5-1% make it through. That being said, if he doesn't apply, the odds are 0. If it doesn't work out, would he consider self-sponsoring flight training? I'd also add that Bristow Helictopers have a sponsored cadet scheme open, so perhaps a worth looking at as well?
Assuming he decides to apply, there are various businesses that help people perfect their application, provide interview prep etc. as well as understand the recruitment process. They aren't cheap, but if you want to give yourself the best chance at succeeding, I'd personally recommend it.
If you do decide to take the leap, good luck.