So my experience when it comes to kibble is,
So I gave 2 of my rabbits Young Oxbow Rabbit food up until they were 1 year old and just followed the instructions on the bag when they were 6 months for the amount.
When I got the 3rd bunny my other 2 were already 4 years old and on Oxbow Garden Select Adult Kibble at the time… I was a naughty Bunny Mom and just said “meh it’s kibble: and my 3rd received adult kibble since he was 3 months old… As for health, there is no difference between all 3 of them but they are VERY good about eating their hay. The vet says they are little athletes when it comes to checkups.
Oh and if you feed the kibble in a treat ball it can also help them exercise at the same time.
Someone once told me mixing the kibble types is not a good idea because what if their supplements double up or have a reaction but I don’t know if that is true you would have to ask a vet