My father doesn't look like (he is) fifty-six (years old).
My father does not look his age.
My father doesn't look like (he is) fifty-six (years old).
私の父は５６歳には見えません。
look：〜に見える
look like：〜なように
My father looks like he is in his early forties.
私の父は、４０代前半の若さに見える。
また、具体的な年齢を入れずに表現する仕方として、
My father does not look his age.
私の父は歳相応に見えません
という表現も覚えておくと便利です！
Your father doesn't look like 56 years old, I thought he was in his early 40s..
君のお父さん56歳に見えないね、40代前半かと思ったよ。
in his early 40s; 40代前半
in his mid-40s; 40代半ば
in his late 40s; 40代後半
年齢の伝え方。
Men in their late 50s are more health-conscious than men in their 20s.
50代後半の男性は20代の男性より健康意識が高い。
おっしゃられている内容は、以下のように表現できると思いました(*^_^*)
My father doesn't look like 56 years old.
「私の父は56歳のようには見えない」
あるいは、
My father looks much younger than his age.
「私の父は年齢よりもずっと若く見える」
のようにも言えます。
以上です。
少しでも参考になれば幸いです(*^_^*)
日本 
アメリカ合衆国 
