To get into specific companies really is hit and miss, but by my calculation:
Any start up carrier less than five years old-college age "I go to school during the week and fly on the weekend", "I'm taking a year off school to see what I want to do.", "I want to get the travel bug out of me now and concentrate on school in a couple years." Jetsgo was an example.
When a start up gets into the 10 year range, those young hotties are now approaching marriage and child bearing years. RELAX, no offence intended, only an observation of fact. They are, at this stage in life, less inclined to go party, more inclined to wear sweats and relax on thier days off with thier spouse and child(ren). CANADA 3000, Skyservice, Air Transat as examples.
Large legacy carriers that are now healthy enough to start hiring again after 5 years: Domestic, multi stop runs. Domestic layovers where the per diem is at it's worst. Flights deemed undesirable are the age old stomping grounds of newbie F/A's that the senior, more mature and established avoid. To factor in reserve F/A's primarily are young, attractive, no seniority, at the beck and call of the company to fly anywhere, anytime is purely hit and miss. The restructured and recently hiring Empire-Air Canada is an example.
I've had my team of sixteen monkeys working around the clock for the last seven years working on these calculations. Don't blame me, blame the monkeys.