I wonder how I even get a shot as a barback tbh and what is expected.
Bartender's assistant. Clean glasses, bus the bar, deliver drinks, clean up messes, occasionally if they're backed up and you're not inept they'll have you pour a couple beers or make some two-part cocktails. A lot of volume bars are looking to hire barbacks but they're usually planning to promote the good ones after a while, so if being a bartender is your goal they're going to want to know what makes you a good fit.
How old is too old to give it a go anyways?
Totally depends on the bar. First one I worked at was a hotel bar, the bartender there was a loud, eccentric dude in his 40s but he could make a good drink. Usually you see the bartenders and the customers tend to be from the same age group. College bars have a lot of younger guys working behind the bar (in their 20s), dive bars tend to get older customers so the bartenders tend to be older too, chain restaurants almost always promote their best servers to work the bar, so you see a few late 20s to early 30s over there.
I wrote about it in
this word wall of a post, if you'd like some more specific tips on how to go about doing it. Mid 20s is definitely not too old, but there are a lot more important things than age. If you
really want it, you'll find a way.