I think it’s usually not recommended to have a big age gap? Like usually if your rabbit is already matured, they tend to not tolerate little bunnies running around so much, but that’s not to say it can’t work.
My first rabbit was a female & was pretty territorial. She bossed all the other house pets around, my 75lb dog was scared of her too lol. None of the dogs would come in my room. I never intended to get a 2nd rabbit, in fact, I honestly thought Mimzy would never accept another rabbit. But my ex had gotten a rabbit about a year after I got Mimzy & he frequently needed me to bunny sit until he eventually asked if I’d keep him. At first, I had come home with the 2nd bunny’s scent on me & I let her smell around. She wasn’t too happy, but she was fine.
I created a divider down the middle of my room, so if 1 was out of the cage playing on 1 half of the room, the other was in it’s cage on the other side of the room…this way, they were always at LEAST 3 feet away from each other so they could smell each other but no touching. I also made sure to give each bunny a stuffed toy in order to get their scents on it. After each bunny had their stuffed toy for several days, I swapped the stuffed animals. The 2nd bunny didn’t mind it at all, but Mimzy was not happy with the 2nd bunny’s scented toy. I also started switching cages, so Mimzy was kept in his cage for a few days, & he was kept in Mimzy’s cage.
Eventually, I stuck them both in the bathtub to see what would happen & Mimzy almost completely ignored him, she just wanted out of the tub which was a good sign, at least she wasn’t attacking him. The 2nd bunny (Obi-bun), was super docile & sweet so I was never worried about him. Bathtub time was switched up now & then to being walking around the neighborhood in a stroller together, you can do car rides, or really anything that might scare them a little bit in order to encourage them to seek comfort in one another. Mimzy every now & then would try to dominate or get into a scuffle with him but he was so good with her, he never fought back. Eventually I was able to put them in pens together outside in the grass. It started to seem pretty bleak like it was never going to work, it took a while, but Mimzy finally accepted him. Now…from time to time, Mimzy still dominated him or bossed him around (poor guy) especially during dinner time. I sometimes had to pick 1 of the bunnies up to prevent her from aggressively chasing him from over-excitement. Other than that, they were great together.
So, if you wanted to try it, I would definitely plan on taking things slow, try the stuffed animal thing & swapping cages several times so they get used to each other’s scent. I think sometimes you can even take some of the other bunny’s droppings & put them in each other’s litter boxes. She may throw a fit to begin with, but it may be worth seeing if she could eventually get used to it?