No. It solves exactly the problem I described. Age-restricted services currently ask users for their age at signup. With AB 1043, it asks the OS, which was given the age at account creation time. Your solution doesn't do anything for this.
If you buy an Android device, you can already do everything you proposed, but that doesn't solve the problem that parents have. Parents want some way to hold services legally accountable for COPPA violations without all the hassle of 100% device supervision. The only way to do that is to require a standard that service providers and OSes can both implement. Just changing a few OSes with low usage that service providers don't know how to integrate with does nothing.