Nothing wrong with keeping a good looking bull calf for your own use, probably not that one though.  If you like his conformation and disposition, why not look for a bull calf from that same cow/bull mating next spring?  If you do use a retained bull calf it is especially important to keep good records so no sire ends up as more than 50% of any offspring. Retaining a good bull calf from a good cow and retaining his best heifers is a good way to improve your cow herd.