I'll be 37 in a month and was just hired by BNSF as conductor. There were prolly 35 people at the hiring session and I'd guess just by lookin at the crowd, 85% of them were eliminated before we began. As long as you look to be in reasonable shape, are not a complete idiot, can show up to work and know what safety is you will be fine. Just my opinion.
A friend of mine was older than 45 (let's just leave it there) and was hired on by NS. He decided he didn't like it and left after a few months. Apparently a non-trivial number of new hires also do the same... if they make it through the process at all.