For a regional, late 30's is a good bet for top guy. At a major, depends. There may be guys coming from the regional in the same age group or older, or Mil guys in their early to mid 40's that just came off a 20 year+ career. Usually a mixed bag.

Aircraft you want, yes. Usually done by class senority. Schedule you want, whole different matter. If for some reason they are sending every newhire to XYZ base, and the schedules there suck, all you are is top of the heap for crappy schedules.

Don't forget, you are still a newhire and at the bottom of the pile in base. When I hired at XJET and transferred to IAH, I was number 500 out of 520. Took 8 months to hold relief/composite/secondary/buildup/mix line, 11 months to hold a hardline, 14 to get weekends off. Mind you, thats because I voluntarily went to IAH. Much better commute, much better trips.