How to calculate age using carbon in array map function?

This application built in Lavavel 5. I had a table with year of birth value. I query the table using this query:

  $tarikh = DB::table('itemregistrations')
            ->select('itemregistrations.lahir_dd', 'itemregistrations.lahir_mm', 'itemregistrations.lahir_yy')
            ->get();

I want to calculate the age using carbon and insert into the collection using array map:

 $tarikh->map(function ($detail) {$detail->Umur = "{$detail->lahir_yy}->diffInYears(\Carbon::now())";
        return $detail;
    });

but the formula doesn't work in string "". How to put carbon formula in the array map? thanks

via Chebli Mohamed