My general rules on being added as an authorized user:
1) Do you absolutely trust them to make every payment on time and not run up utilization? If no, don't do it.
2) Will you be taking a hit on AAoA? You mentioned that they were new. If they're newer than your AAoA, then proceed to rule #3. If they're much newer than your AAoA, don't do it.
3) Do you have a direct need such as bringing down your utilization or increasing your AAoA? If not, don't do it.
One of the false myths in credit is that you must have more to get more. Someone can get exceptional credit by having three cards, two of which report zero balances and one that reports a small balance, plus an installment loan with preferably under 39% of the balance remaining to be paid. As long as you keep the negatives off your credit, those four accounts are enough to age and build your credit score nicely.
Being added as an authorized user should 1) Raise your AAoA, or 2) Bring your utilization in line, or both. If not, it's a good rule to never take the risk. The benefits can be minimal or even nil while risking actual damage by putting your credit destiny in someone else's hands for a time.
