It's great that you are riding!
The idea of trying to ride with other groups is a good one. Do you live in an area that has several bike clubs? Usually there are a few people that will give you pointers, if you let them know you are new to cycling. Get there a few minutes early and ask some questions. It's pretty easy to ride a bike, however it's difficult to ride well and requires many skills.
Don't forget that cycling is fun. Try to have some fun on the days that you ride without a group.
It's not politically correct but women are at a disadvantage. We are smaller, have less muscle, carry more fat percentage wise, and have smaller lungs and heart.So keeping up with young 20 something bucks was never possible for me in my 20's. I could ride with the men's masters. However, I see really excellent women out there that can hang with the men. Things have really changed in the past 25 years.
There are some good books out there, Lance Armstrong has one that is easy to understand.
Do you have a goal in mind with what you want to be able to do? Do you want to enter a triathalon, ride a century, or race?
If you have some discretionary spending money, you could hire a coach. Some people on this site have done that and reported good results. It might be the quickest way, if you are in a hurry and have a specific goal to achieve.
Cycling is a sport that does cost money. Do you have a decent racing style bicycle? Unfortunately, you cannot buy speed.
It does take time to build up your lungs and legs and rest of the body. My first ride I did about four miles and boy was my butt sore!
A good rule of thumb is to increase your weekly mileage by no more than 10 percent. In a few months it will be easy to do a 50 or so mile ride. Try to work on distance build a foundation before you try to work in speed. Be sure to bring snacks for rides longer than two hours and drink before you get thirsty. Know how to change a tire and fix a flat.
Every day is a blast, bike commuting, running errands, and in the summer bike touring. Mostly I ride alone, but lately have been riding with a triathalon club on Saturdays.
Be patient with yourself. Hopefully you have found a new sport that will last your entire life and an new lifestyle. Have fun!