Yondu wasn't one to judge a child for having a weapon. He had Peter flying ships and firing guns by twelve. Yondu himself could break a grown man's neck with ease at eight. But the tragedy of the situation isn't that Ken can do it, it's that it's necessary for some reason.

"Careful with the practice skewer, boy. You never know who's gonna rush right through an' clothesline themselves on it."

No commentary on age. Just the knowledge that if there is a spear, or a broom, or anything with a long handle eventually someone is going to get their dumb ass tangled in it.