I don't understand this option.
Have you ever noticed that if you don't select "require exact age match" on your targeting, your audience will be larger than if you select this option.
It seems logic, because, if I understand well the concept, when I don't select this option, I'll target people that just turned age+1.
But why I've always a larger demo targeting (with keywords) :
- 40-42; "require exact age match" not checked (~120k audience)
than targeting :
- 40-40; "require exact age match" checked (~25k audience)
- 41-41; "require exact age match" checked (~25k audience)
- 42-42; "require exact age match" checked (~20k audience)
- 43-43; "require exact age match" checked (~20k audience)
==> (~90k audience)

If someone have an explanation... 
Have you seen some differences in your split testing with or without this option?
Julien
If you don't select the option your demo will increase: 4/5 years younger & older.
^^
As said if you pick broad age ranges you get some leeway both younger and older, say for example you did a dating campaign that was 30+ only but didn't choose exact, you would be showing your ads to people under 30 too.
Thank you for your answers guys.
Whoa, I'm shocked, I didn't know that it would target so broad :S
Have you noticed any advantage to not use" require exact match", as they say you pay the extra bids at a discounted price?
I think what FB meant for 'you pay the extra bids at a discounted price' is your ads get shown to more people, at a bid price that is below the bid price if you choose 'exact'
As for me, what i experienced was, if i didn't select 'exact', and i was targeting an age demo of 30-39, my ads do get shown to people who are below 30 years old.
How do i know this? The ad network actually pays a lower payout for signups who are below the age of 30. Hope this make sense.