How do you catch Aerodactyl in Pokemon FireRed?

Answer 1

The Amber you get in Pewer city will be revived into a Areodactyl at the Cinbar research center.
In Pewter City go to the musuem on the right you will have to use the HM cut go in the little house and talk to the guy with the golden rock and it will be called the old amber.Take it to the fossil regenerator in cinnabar island wait out the door for a few seconds and he will give you Aerodactyl at Lv 5

Answer 2

You don't catch it you get it by resurrecting the old amber fossil at the cinnibar island lab. The old amber is obtained in the pewter city museum but don't go in the normal entrance instead go to the path to the right use Cut and go in the side entrance talk to the scientist near the bookshelves and he will give you the old amber. Take that to the lab on cinnibar island and show it to the scientist running the resurrection machine (he's in the last room) once you give it leave the lab and then re-enter and talk to the scientist again to receive an Aerodactyl.