I'm sorry, I have to brag a little...

[Eden]

I just need a refresher her on US cats... Cat 1 means you've made it onto the standings? and the bigger the number, the faster you race?

So a beginning racer might be cat1, and elite racer might be cat5?

So categories are based on ability?
Or are cats then age-graded as well...

So you might be a Vet1 woman (thats me - age 41) but you could be a cat2 racer?

Other way around Cat 4 is beginner for women (men have one more so start as Cat 5's)
To move up you need to get points. If the race meets certain criteria (enough competitors and a long enough race) points are awarded 1st -7 points, 2nd 5 points, 3rd 4points, 4th 3 points, 5th 2 points, 6th 1 point.
If you get 20 points in 12 months you qualify for an upgrade, 30 points in 12 months is often a mandatory upgrade, but because around here you go from racing cat 4 to completely combined 1,2,3 fields usually upgrades are not forced. You can also request an upgrade if you have a certain number of finishes in qualifiying races.
TT's never get upgrade points, only mass start races.
if you are over 35 sometimes you have the option of racing in the Master's category. For women there are usually only 2 master's fields A - for over 35 and a cat 1,2 or 3 and B - over 35 and a cat 4.