As of September 1, 2019, American Express is only allowing cardholders to transfer Membership Rewards to partner accounts of authorized users and those authorized users need to have been added at least 90 days ago. What does this mean?
You still are not allowed to transfer (or pool) Membership Rewards between accounts, even with your spouse, family member or authorized user(s). This rule is more restrictive than Chase and Citi, which both do let you send points between accounts.
What you can currently do is transfer Membership Rewards points to the partner accounts of people who are authorized users on one of your American Express cards that earn Membership Rewards. For example, I can transfer Sharon’s Membership Rewards to my Delta SkyMiles account. I can also send my Membership Rewards to my dad’s ANA Mileage Club account, which is exactly what I did to help them have enough miles to book their trip to Bali and Thailand. When I did this, I added him as an authorized user to my account and a day later I could transfer the points. That’s no longer possible due to the 90-day hold period before you can make transfers to new authorized users.