Once you get into your 30's, your endurance decreases little by little, so you can't stay up late at night like you could when you were younger.
この場合、次のように言うのが自然で良いかなと思います。
ーOnce you get into your 30's, your endurance decreases little by little, so you can't stay up late at night like you could when you were younger.
「30代になると、体力が少しずつ落ちてくるので、若い頃のように夜更かしができない」
to stay up late at night で「夜更かしをする」
ご参考まで！
カナダ 
