buck age at first breeding

The first time we wanted to replace our buck, we were uncertain about when to try breeding. With does it was easy to check their color (thanks to RT for teaching me that). The advice was to breed does as soon as they were 'ready'--at 6 months or earlier,, but to wait for the buck to reach at least 7 months and maybe longer because if he was intimidated (or even attacked) by his first doe, he'd be unwilling to breed later.
We 'cheated' a bit with Beau--I think he was just short of 7 months and we put him in with an experienced and easy-going doe. No problem. This morning we tried a doe that is starting her 4th season of breeding with Cloud, just a couple days short of 6 months old. He backed into a corner briefly to think things over but then mounted twice. OF course we won't know if he was successful for another month, but we start breeding for early spring litters after taking the winter off, and the sooner we can figure out if a new buck "works" the better. On our small scale it doesn't make sense to keep more than one buck and we're more apt to find someone to buy Beau to start their own rabbit raising project early in the growing season.
Hope that is helpful to someone just starting and wondering when to breed a young buck.

I've let them try as young as 4 months with a gentle doe. It's a 50/50 chance I've found. Some are very shy and cower, some know just what to do! I generally wait until 6/8 months though.

I've had good luck with my rex crosses between 4 and 5 months.