I know for a fact it's 30 in Yellow, but I'm not sure about later Gens.
In Red and Blue, plus it's remakes, it's level 5. In Gen 2 it's 5 I think You can't get Aerodactyl in R/S/E, unless by trade In Gen 4 it's level 20. In Gen 5 it's either 20 or 25 In Gen 6 it's 20
Hope I helped!