Oneworld airlines American and British Airways have San Francisco to Amsterdam at $553 round trip for travel from October to early May 2018. The price drops to around $508 using the AARP discount link.
As a reminder, you do not need to be 50 years old to join AARP. Simply pay the $12 membership fee, then login to the British Airways AARP discount ticket booking site.
British Airways AARP discount ticket $507.68 round trip
San Francisco SFO – London LHR – Amsterdam AMS – Philadelphia PHL – SFO