Fair points there Pete, it's more as they would be young - 7days+ and on milk so I think a combined group might end up with the older ones bullying around the feeder, and later on the bull would be in with the older group. I was thinking that the calves can run ahead and eat all the seed heads etc that help their rumen to develop and the older ones could be held tighter to trample better. I do run one or two retired dairy cows and their calves with the calves which helps to keep them well behaved and possibly teaches them grazing too. I would like to use some old cows and multisuckle, but it's difficult to justify loosing some grazing against feeding waste milk which is effectively freeThe other consideration with calves is that they learn the art of foraging from their elders - just as "mum" taught us to peel potatoes and cook them. Watch newly weaned lambs etc, they haven't a clue what to do for a while, and it checks them.
Your calves may actually benefit from running with older stock, not only for learning and "herd stuff" but also to help them build immunity via exposure .