No, not all even numbers are composite. The number 2 is even but prime—it is only divisible by 1 and itself, meeting the definition of a prime number. All other even numbers are composite because they are divisible by 2 in addition to 1 and themselves, giving them at least three factors.
A composite number is defined as a natural number greater than 1 that has more than two distinct positive divisors. For example, 4 is even and composite (divisors: 1, 2, 4); 6 is even and composite (divisors: 1, 2, 3, 6); and 8 is even and composite (divisors: 1, 2, 4, 8).
The key exception is 2 itself. Since 2 is only divisible by 1 and 2, it has exactly two divisors and is therefore prime, not composite. This makes 2 the only even prime number. Every other even number—4, 6, 8, 10, 12, and so on—is composite because they can all be divided by 2, plus they have other factors as well.
So while the vast majority of even numbers are composite, the statement "all even numbers are composite" is technically false because of the single exception: 2.