EBikes and Age...

Hmmmm......I was racing motorcycles at 5yrs old. I can't see how an e-bike would require more age or experience than a motorcycle to operate off road.
I think those electric cars you can buy for kids at Walmart have some kind of age warning, so sure, limit them by age, but it won't matter much cuz there really isn't a market for child size ebikes.

I think skateboards are more dangerous than bikes, ask any ER provider and they'll say the same, but skateboards are for kids, so go figure.

I think a lot of how and what we regulate is silliness, but I only have one vote.
The Netherlands has observed a significant increase in injury rates and severity of injuries with older/elderly e-bike riders (usually males, no surprise there). It's believed that the e-bikes are simply moving faster than their observational or reaction times. Also, the injuries are worse as the bikes are moving much faster than they would be for those riders on a human powered bike.

And e-bikes are heavier and do more damage to what/who they hit.

The same issues could occur with someone younger. Perhaps a speed limiter is a good idea until someone gains more co-ordination, riding experience and traffic/trail sense.