How old does a calf has to be before you switch it from calf feed to corn?

A calf should be at least 3 months of age before you can deworm it.

Pretty well any age, really. Bobby calves (those that are a few days old) can be sold for veal (but this is primarily limited to dairy, not beef cattle). Baby beef calves are those that are from 1 to...

A calf can get calf starter a few days after he's born. Some like to hold back until a few weeks prior to weaning.

Preferably two months of age, though it can be branded when it's as young as a couple weeks old.

That is actually irrelevant. A calf is called a calf until it is around a year of age, until then it is called a heifer, bullock or steer. A heifer is called a cow until after she's either had her...