Because the first letter of word "old" is "o" and "o" is a vowel pronunciation letter and we use with any vowel pronunciation letter article "an". So,here an old city is right.

Beauty is evergreen.

I cannot talk to right now, I am in the hotel, I am going to eat food.

Right

In

Aviation means the flying or operating of aircraft.

wah mera bhai h.

Right

tm kha ja rhe ho?

How is your class going on?