Ten years ago most 121 companies wanted, ATP, and at least 1000 hours of pure jet time. Turboprop did not count. Now, things have changed, the ATP is still a must but the turboprop restrictions have been deleted. Age wise, young or old doesn't matter. I know of pilots in there mid fifties have been hired, (most will never see the left seat.) The four year degree is desired but not required. As for pay, that is also a supply and demand. In the 1980's there were lots of pilots in the market. Today the number has almost disappeared. Get an ATP, fly for a regional for a couple of years and you will be very attractive to any of the majors.