Yes, some advertising will likely work better for some age groups than others. It happens. It is a part of well thought out advertising.
The thing is that they weren't targeting the "right ad to the right user". It isn't like they were customizing ads to different groups hoping to increase their diversity. They were only targeting one group of people and excluding others upfront. No trying to show the ad to older folks nor investing in an ad for those folks. And even if you produce multiple ads targeting multiple ages, it is probably prudent to simply show them to everyone over 18 in the area you are advertising in - just to be on the safe side of the employment laws.
The thing is that they weren't targeting the "right ad to the right user". It isn't like they were customizing ads to different groups hoping to increase their diversity. They were only targeting one group of people and excluding others upfront. No trying to show the ad to older folks nor investing in an ad for those folks. And even if you produce multiple ads targeting multiple ages, it is probably prudent to simply show them to everyone over 18 in the area you are advertising in - just to be on the safe side of the employment laws.