does it get easier later on?

I'm currently debating on whether or not to go into finance. I read a lot and I think the general consensus on how to break into wall street is to get an entry level i-banking job. However, I do know there are long hours associated with the entry level positions. However what happens when you are 30 years old? Or 50 years old and can't handle those hours? Is promotion just a crap shoot or is it based on meritocracy and network? I asked around and didn't really get a solid answer.