How young is too young?

Kelda 3 yrs old Jackson Hole

So I am curious as the discussions has risen with a friend because her grandson was injured it is a sad thing and I do feel for him...side note he will be ok. But this led me to wondering....Just how young do you think is too young to have your child on things such as 4 wheelers, horses, snow machines and the like?

I know many that have their little ones on horses, 4wheelers, snow machines etc. kelda was on her first horse ride at 4 months old and on snow machines at 13 months old, 4wheelers by 5, cross country skiing 9 yrs and water jet skis age 11. Anything can happen at any age so I don't know mixed emotions I guess on how one feels and believes. i was a nervous wreck at first because well she was my first, but Carl was a trail guide and snow machine guide for years and definitely wouldn't put his own child at risk. If he hadn't thought the horse he was riding was safe he never would have put her in that position. At 2 she was at a birthday party and got upset that the person wouldn't let go because she knew what she was doing...A horse tried to buck her off when she was 3 and this kid wanted to ride again...lol. She never let go she held on with all her might. We shifted horses and let her back up. So I mean yes things happen but sadly we can't put them in a bubble forever.