My kids were authorized users in our credit cards since middle school. ( I know sone kids that age can’t handle it but our had no issues). In college they both remained so. But my daughter who went to Michigan was able to get her own CC because PNC bank had a relationship with the college. I’m sure the interest rates were outrageous but who cares. Both my kids were taught to pay cc weekly to help track spending. Interest rates were irrelevant.