That's strange. Isn't she a little old to wear that hairstyle?
Shouldn't she have a more mature hairstyle at her age?
That hairstyle is for someone a lot younger, isn't it?
その歳でその髪型はどうなの
What about that hairstyle at that age
変だね。 彼女はその髪型を着るのに少し年をとっていませんか？
That's strange. Isn't she a little old to wear that hairstyle?
彼女は彼女の年齢でより成熟した髪型を持つべきではありませんか？
Shouldn't she have a more mature hairstyle at her age?
その髪型はもっと若い人向けです。そうですか？
That hairstyle is for someone a lot younger, isn't it?
I'm not so sure about a woman her age wearing her hair like that.
この場合、次のような言い方ができますよ。
ーI'm not so sure about a woman her age wearing her hair like that.
「彼女の年齢であの髪型はどうなんだろう」
I’m not so sure about ... で「…は考えものだなあ」というニュアンスです。ここでは「彼女の歳であの髪型は考えものだなあ」という感じです。
ご参考まで！
アメリカ合衆国 
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