They are never too young. Apple's ecosystem is designed for each person to have their own AppleID. Family sharing is what you'll use to share purchases with family members.
Instead of sharing an account with your child, which can give them unwanted access to your personal data, create an Apple Account for them. Then you can easily set age-based parental controls, and they can use Family Sharing, Messages, the App Store, and other Apple services.
support.apple.com
It doesn't work well enough at all for small kids.
Every good kids app has in app purchases, many of them are tied to my Apple ID without a family share option. I have running balances of Apple gift card to pay for these apps and subscriptions. With 3 kids under 7, I just want them to all be on the same page. We end up spending a pretty good amount on this, in small doses over time.
Similar for purchased iTunes TV/movies. The "sharing" feature for family is not great. You have to go digging through purchased history to see the shared library, it doesn't flow the same as for the native account holder to just open the TV app and see our library of hundreds of videos. Too complicated to have an Apple ID for the kids and do that. My wife can barely figure it out, she has a separate Apple ID, of course. They want you to go in and download your family shared video content to your device, you can't even stream it.
I pre-ordered myself some Alexa earbuds which will be paired solely to my iOS and iPadOS devices, retiring the AirPods. No other choice. Submitted feedback to Apple, should be able to disable AirPod pairing to certain devices.