The Senior cards are eligible to participate in Membership Rewards, but there is an additional $40 program fee.
Start here:
http://www.membershiprewards.com/cat...rmsSplash.aspx
Scroll down to paragraph 2 WHO CAN USE THE PROGRAM & ANNUAL FEES, and look at the table.
Did you ask if Customer Service would transfer the points from the account you are closing to the other person's account on a one-time exception basis? They may be more willing to do this if the closer is an Authorized User on the surviving Platinum Card account. You don't have to choose a supplementary Platinum card ($175, for up to three). Instead you could request a Gold card ($45, for up to five).