Why, is the law going to be updated with a regular expression?

1) Increased unemployment in the adult segment, due to teenagers stealing their jobs.

2) Need for government agency to enforce the age requirements. Modeled after immigration authority, such agency would need to be able to raid the businesses in order to do age verification, to ensure that teenager-compatible jobs are not given to adults. Also, such agency needs to ensure that people are fired on the day they reach 20th birthday, and thus lose the "teen" status.

I don't think you need the second part - the only requirement is that the older people be payed more.

If they have not received raises after spending many years with the business, then it's unlikely that their years of experience matter.

And if their years of experience do not matter, they would be replaced with lower-cost younger labor well in advance of them reaching particular age group considered "older".