Flying really is a young mans game these days, for a number of reasons. Firstly the pay is pretty crap when you take into account the loss of weekends, Christmases, kids birthdays, important events, getting up early being away from home etc etc.
Younger pilots starting say in their early to mid 20’s have the age advantage. By that I mean they can take a job to build their hours and then move on to a better carrier not caring about things like seniority. They could get a few thousand hours in Ryanair and jump across to someone like BA (assuming they were hiring), sit in the RHS for arguments sake for 10 years on a 777 seeing the world and then still only be in their mid 30’s when command comes around. Seniority isn’t really a factor for them as they will have approximately 25-30 years in the LHS once promoted to move up the list and enjoy all of the benefits that entails. They could also have spent a few years in the sandpit building up their experience before heading back to Western Europe. Nothing would have been wasted as they were young enough to enjoy the experience.
Remember that the days of quick commands are gone for now. There are long lists and a wait of 8-10 years at most of the airlines these days as recruitment and expansion has dried up. ICAO has pushed out the retirement age which means the guy sitting in the LHS isn’t going anywhere fast. Even more so since their pension has probably been decimated in the current recession and they will need to be working longer to save for retirement. That means you will be in your mid to late 40’s at the earliest before you see a command. You will more than likely be flying as a 40 year old f/o with a captain who could be 10 years or more your junior and will have 30 years of sitting in the LHS that you want so much. If you decide to switch airlines then you drop to the bottom of the seniority list and may never see a command and be a career f/o so to a degree you will be hamstrung.
Now I am not saying that anyone in their mid 30’s or later shouldn’t become an airline pilot but please be under no illusion of what you are getting yourself into.