It's always good to have a girlfriend period. (Assuming you enjoy each other's company).
There is no "one size fits all" when it comes women or men for that matter. Health and attitude are probably more important than age differences. People often say of mixed age daters; “What do you have to talk about?” As if all older people are "out of touch".
Most conversations have to do with likes and dislikes, upcoming events, news events, disappointments, weekend plans, TV shows, movies, weather, where to eat…etc The majority of people choose to live their life in the (present) and not in the past regardless of age.
The vast majority of people select friends and mates that have common threads. It’s fairly unusual for someone to date a mature person and at the same time have a “best friend” who is running around giving people wedgies! Our best friends and significant others are normally people we share the same values with.
Having said that it's important to remember: (most) relationships fail! If they did not the majority of us would be married to our high school sweethearts! There is no reason to get caught up on age differences when in fact the odds are the relationship was not going to last a “lifetime” even if you were the same age! Live for today!
If you are not on the same page at some point in the future regarding the relationship or one of you commits a "deal breaker" then you will go your separate ways. This happens with all couples regardless of age. Best of luck!