Here's the "official" rules:
Footnote #1 - Basic Cardmember (cardmember) may apply for a Priority Pass membership. PP membership is subject to approval by Priority Pass Limited and is not guaranteed. Unless cancelled, PP membership automatically renews on its anniversary date. PP membership may be cancelled by American Express if: (i) the Priority Pass benefit associated with the American Express AeroplanPlus Platinum Card is changed or terminated, or (ii) the cardmembers AeroplanPlus Platinum Card is cancelled. PP membership includes access to any airport lounge participating in the Priority Pass Program. Participating lounges are owned and operated by independent third parties and their participation and/or facilities can change from time to time. To access a lounge, the cardmember will need to show his/her valid Priority Pass card and an airline ticket for travel on the same day for the cardmember and each of his/her guests. At their sole discretion, participating lounges may restrict entry to persons under 21 years old, please check restriction details for the individual lounges at www.prioritypass.com or your Priority Pass Directory provided by PPL. All lounge visits are subject to a fee of $27 US per person per visit. This fee applies to the cardmember and his/her guests. Lounge access charges can be billed by PPL to the AeroplanPlus Platinum Card connected to the cardmembers PP membership upon PPs receipt of notification from the lounge visited. Any US dollar charges to the card will be converted to CDN dollars using a conversion rate and applying a conversion commission as specified in the Cardmember Agreement and Disclosure Statement. All cardmembers are also subject to PPLs terms and conditions for the Priority Pass Program and the individual lounge operators terms of use for the participating lounges visited. For complete PPL terms and conditions and a directory of participating lounge locations, please visit: www.prioritypass.com.