True, but the only source that states Hagen's age is the novel.
The novel also specifically states that Hagen and Sonny were the same age.
The novel makes a lot of specifications, like Vito being 25 in 1919 en then being sixty during the Dons meeting, contradicting his age. Also, the novel later states Sonny was sixteen in 1933.
According to Part II, Sonny was born in 1916, so we can assume Tom was too.
