It might be before they are born. Super popular email services like Gmail are still somewhat of a land-grab for getting names that aren’t saddled with awkward extra characters or numbers. If you can get a good full name, many do.
Technology sometimes forces us into it, so they can have important accounts:
Like Apple or Facebook. Chris Enns needed one for his kid in 5th grade to set up Xbox and other gaming related things.
Sometimes we do it for the most beautiful reasons:
10-11 Years Old
This seems like a common age.
Facebook requires you to be 13 though, so I bet that’s another common cliff.
5th or 6th grade seems to be the most common right now. For me (born 1980), I think I had one (probably AOL) in high school, but the first one I used heavily was the one they gave me in college. At the end of college I set up firstname.lastname@example.org and that’s been my main ever since.
How old are you now and how old were you when you got your first email? How about your first email that you actually used?