You would need to quarantine him for at least 30-45 days before you turn him out to your hens. They may not like him right off bat but after a few shuffles, they will be ok. Check for mites and lices, deworm him while he is in quarantine. He would need to be far away as possible from your existing birds in case he does have something like CRD or any contagious diseases or worms or lice/mites.
Yes why is he free? Disposition is important too or too old or too aggressive with the hens can be determintal to your flock and as well as yourself. You do not want a roo that is nasty, spurring behind your back, or infertility after incubating so many eggs that there is no viable chick in the egg.