at the age of 23 =((米))at age 23
23歳で
at the airport
空港で
at the all-in cost
全部込みの経費で
at the appointed hour [spot]
約束の時間[場所]に
at [in] the back of one's mind
心の片隅に,心の奥で
at the ballot box
選挙で
at the barber's
理髪店で(◆くだけた表現ではat the barberも用いる)
at the beginning of the month
月初めに(◆inなら上旬)
at the beginning of the month
月の初めに
at the bottom end of the street
この道の行き止まりに