What’s an alternative term for “age groups”?

Probably a showdown:

• An event, especially a confrontation, that forces an issue to a conclusion.

or a clash:

• An encounter between hostile forces; a battle or skirmish.

(from TFD)

The expression the early bird catches the worm can be used to convey the idea of not wasting too much time sleeping:

• Prov. If you wake up and get to work early, you will succeed. (Sometimes used to remark that someone is awake and working surprisingly early, as in the first example.) Fred: What are you doing in the office at 7:30 A.M.? Jane: The early bird catches the worm. I didn't expect to see you studying at the library at this hour of the morning. The early bird catches the worm, huh?

(McGraw-Hill Dictionary of American Idioms)