Checkout the United profile within APC. It has bases, number of aircraft, pay scales, and a remotely close indication of the most junior CA aircraft type and base (like it says SFO 737 march 2015 hire). In 2019, the junior upgrades were going to SFO and EWR, and approaching the 2yr FOs. In more desirable bases, upgrade on the 73 was more like 7~15yrs. In IAH, you might finish a career before upgrading into anything for example. If LAX ever recovers from COVID, that might be a nice trade off for a junior pilot to upgrade before turning completely grey. However, don't be discouraged because this could all change either way in the blink of an eye, or launch of a hyper sonic missile.