My daughter will, on occasion, take her 10 & 8 y/o girls along with the five year old boy on what I consider longer rides. As long as he is with everyone his energy level remains great but as soon as he is left with either of the girls the energy level is rapidly depleted as he finds other things that are more fun.
On a personal level I would put him on an electric bike right after I decided to shave with a chain saw. My wife has purchased electric vehicles for each grandchild when they were VERY young with this grandson as an exception. None of the children had the eye/hand coordination to safely operate the vehicles and these were "Barbie" jeeps and a "John Deere" thing with a trailer for one of the other grandsons. The girls were around five with the boy at four.
The primary result was the vehicles cluttered the garages of their parents. They required supervision at all times, something that was seldom available and the batteries would go dead from lack of charge. I do believe that given sufficient training they would have been able to use them but quite frankly even the kids became bored at three MPH.
Against my advice the oldest grandson was given an electric scooter, with a seat, at age six. This is a big boy, he looked eight or nine and had played soccer for two years. Within five minutes he had scrapped both knees, both elbows and dented the helmet. As expected he lost interest and I have no idea what happened to the scooter. He rides and enjoys his bike and I enjoy buying him the fancy new model every now and then as he shares growth spurts with weeds.
What all of these kids need is exercise and a regular bicycle provides that. The child has a feeling of accomplishment from learning to ride and gaining the stamina it takes to make distances. With the way the world is today it's not really possible to simply turn a child loose without supervision. To me it's amazing when I take the girls with me on a ride. They will ride five miles and beg for more.
But, this is for your child and all I have is an opinion and a little experience albeit with my grandkids rather than my own as all they had was regular bikes and back then it was safe to turn them loose in the neighborhood without fear of predators.
Good luck,
Mike