Just going to pretty much agree with what has been said.
The best thing is to go to results of local club races and look for the length of races you are looking at.

Some of these may be listed by distance only, but it will give you an idea of womens times albeit in unknown age groups.

If you go to club champs results, or nationals, they will be listed in age categories and will give you an idea of what to aspire to.

The goals you set yourself and the speed you want to do will really depend on the skill level of the riders you ride with and the terrain of the various rides/races.

I suggest you go along to the next meeting of your local club and have a chat to either some of the women there, or to some of the male riders aged in the 30's/40's and older... they will give you a good idea of where and how to begin. (I say males of that age because they have got over their self-importance, and are genuinely interested in you as an aspiring cyclist first rather than as a woman)

Without knowing your skill level, I suggest you start in the lowest grade and get a feel for it... these are the novices and newbies and those who are not there to ride more competitively. If that is easy, ride up a grade the next time.

The advantage of club riding is that it will also teach you race and pelaton protocols too