Advertisers don’t pay for impressions with 50 and 80 year olds.
Facebook needs 18-35 year olds to be engaged, or the ad dollars will dry up.
Advertiser demographics are quickly shifting as the baby boomers are hitting their 50s and 60s.
There’s a certain point in hitting the masses where the age group stop mattering. FB, with 1/9 of the planet signed on, is way past that point. An advertiser will hit lots of members of their target market on FB, just because there’s so many people.