Question in the title really? What age should a colt be seperated from fillies and mares? Could an 6 month old colt run with the herd until he is cut in october? x
They can serve a mare from 6 months...I wouldn't risk it unless you want the pitter patter of tiny hooves!!!
Remember that after they have been cut they can still "perfom" weeks afterwards so it may be better to either get him cut as soon as he drops or find other boys to go out with