Average isn’t a very helpful term, and can have a few different meanings, mathematically. Better to use mean, mode or median.It doesn't work like that.
If 10 people are born on the same day and one dies after 12 months but the others all live until 70 years old the average lifespan of those 10 people is 63 and 90% of them exceeded it.
If 9 of them died at 12 months and only one of the group reached 70 the average lifespan would be 8 years (or just under to be exact) so only 10% were above average.
Average does not equate to half, it can but not necessarily.
Not picking on you particularly, I see a lot of people making the same assumption.