I personally know a 3 year old QFWP member, and she's held black cards since she was a new born thanks to Mummy and Daddy's fortnightly trans-pacific crossings.
Slightly off topic but slightly related also I suppose. Does a child of gold or higher status or traveling in their own seat in J or F have lounge guesting rights?
For example if I take my 3yo son in J with two non-status PAX in Y can my son and I guest them both into the lounge? Will it differ depending in airline/location?