For me at age 10 my children should understand the market and how it works, interpreting chats and deciding the next move of each coin from studying the price action of different coins. At age 13 the should start trading with a demo account and at age 15 they should have funded their first account. This would help them become financially independent, also help then limit future gambling prowess and also make them prepared for their careers
managing business is also a good way to teach kids about the value of money. they can also see how hard it is to earn money. but trading, this needs a lot of mental and emotional preparation for your kid. if you want to start early, use small funds, don't push them. let them learn on their own pace. i can't say what age is early because it depends on the capability of the kid. some are mature enough to look at their situation on hand while others are still in the easy-go-lucky stage. the emotional part is very crucial as some of them can't handle the stress brought by this activity.