After a concussion, when can teens return to the football field?

Honestly, I do not know much about concussions over all. I do know they can cause death though. The information that Mr. Brian Mahaffey wrote about the days off after the healing of a concussion is brilliant if you ask me. Especially by narrowing down by age. From what I read in this article concussions are more serious than I expected. Seems like there is endless possibilities of what could happen to the victim of a concussion. I only played football through middle school so I wasn't around sport related injuries much. The only injuries I had in sports are a sprained wrist and a cracked knee that led to crutches. So are concussions a common thing? How do you heal a concussion? These are things I don't know of. That's why there is a Google I guess.