Even when I've used the AmEx Plat for PC access, I was allowed to bring my family (spouse, 2 kids)! So, definitely an 'under 21' can be guested into the PC, they simply are not permitted to be the primary member! My understanding is that -- depending on the method of access to the PC, -- ie. PC membership, reciprocal partner benefit, or *Gold status (non-domestic partner) -- the number of guests varies according to the program being utilized.