こんな、少女と言っていい歳の女の子が殺し屋だと?
I'm wondering if there is an omitted particle between the bolded いい and 歳 of the above sentence, which is the last sentence in the provided context below.
Context: Narrative character is thinking about another character named "Ein" (Ain in katakana).
アインの歳は幾つだろう? たしかに大人びた印象はあるが、どう見てもまだ子供だ。こんな、少女と言っていい歳の女の子が殺し屋だと?
I can infer the いい is most likely connected to the 言って as 言って is being quoted with the と particle; and the 歳 is connected to の女の子. Is there an omitted particle in the above sentence; and if there isn't, what is occurring in the bolded section of the sentence?