The sum of ages of Will and Annette is 20.
If Will is 4 years older than Annette, how old is he?
How old is Annette?
Let x be the age of Annette.
Will is x + 4 years old.
The sum of their ages is x + (x + 4) = 20.
Combining like terms, we get 2x + 4 = 20.
Subtracting 4 from both sides, we get 2x = 16.
Dividing both sides by 2, we get x = 8.
Thus, Annette is 8 years old.
And Will is 8 + 4 = <<8+4=12>>12 years old. Answer: \boxed{12}.