PF has its easy formula. 3.5 has +3 HD/natural armor an age category, with usually +2 to Str and/or Con (Str sometimes gets more, especially if size increases, Con sometimes gets +0), and +2 to mental ability scores every few age categories based upon dragon. Fly speed increases by 50-ft but loses a maneuverability grade sometimes when a size increase is gained. DR is gained at Young Adult and increases by 5 every 2 categories afterward*. Spellcasting starts at 1st and increases by +2 Sorcerer levels per age category thereafter. Breath weapon damage is nxdy where n is the age category, x is normally 1 or 2, and y is a type of die. SR is Z + CR.

Honestly true dragons aren't that hard. I've just done too many and they bore me. I mean it'd be easy to find ones that match people very well (Red Fel, LoyalPaladin, Iz because Snowbluff and co have been corrupting the monk, NeoPheonix... I mean I'm already a true dragon apparently if you make your avatar a peanut dragon it will get requested).