。
The problem is that you're too young.
Literal
Problem [topic-は] you [subj-が] too-young [quotative-と] say thing [copula-だ].
と言う事 is an emphatic spelling of ということ — the kanji 言う makes the quotative layer visible, though modern usage typically writes this in kana. Functionally equivalent to a bare ~事だ but with the explicit quotative framing pulled out.