More than a year ago, I think it was possible to get the discount without being an AARP member by going through the AARP gateway. Since then, at least in my experience, I've had to log on to my AARP account before the AARP website will redirect to the BA website with the discounts applied.

The barriers to getting the discount are not high: $16 per year for membership and as others have noted, no age requirement for membership--although I now comfortably meet the target demographic AARP seeks.