We have a rabbit that is about 7 years old and we haven't had another rabbit with her, her entire life. Could this be a potential problem if one could be older than the other considering the girl rabbit be older?
The age of the rabbits have little bearing on bonding. Our first bond was a 3 year old female and 7 year old male, it was very easy. The male very much wanted to have a friend and he wanted to groomer her as much as she wanted to be groomed.
I STRONGLY Recommend
You don't just bring a bunny home and expect they will eventually be friends with your existing rabbit. Bonding rabbits is hard, and often does not work, you end up with two rabbits who can not be left alone unsupervised. Have a date so your bunny can pick her own friend. Our local rabbit community works with the shelters to provided an experienced rabbit handler to try introducing different potential partners so you can make the best choice.
Before attempting to bond rabbits both should be spayed or neutered for at least 4 weeks before any contact.
You don't say if either is spayed or neutered, the above assumes they both are or will be. If they are not 'fixed', you can't leave them together.
If you are planning to put them together only for breeding, then your female rabbit at 7 years old is to old to be having babies. Imagine your 70 year old grandmother having a baby!