、。
My lovely friend, to me you will be forever young.
Literal
Beautiful [of-の] friend [vocative-よ], me [to-にとって] you [topic-は] forever young [copula-のだ].
Literary, poetic register. 麗し is the classical い-adjective 麗し (beautiful, lovely), preserved here in its archaic form with の instead of the modern 麗しい. The ~にとって pattern ('to/for X, in X's view') frames the whole following clause as the speaker's perspective. のだ at the end adds explanatory emphasis in literary speech.