Cows?? You mean steer calves, right? A cow isn't a cow until she's had her second calf, you know. And a cow is a FEMALE bovine, not male.
But, that aside, I think it would be alright to put them together. Just be careful during feeding time though that you feed them in two separate groups, because the two-month-olds will be more greedy and pushy than the young calves. Also watch that the two calves don't start trying to suckle on the older calves either. If that happens, then you may have to separate them.