flametitan
Explorer
You can, you just suffer the consequences after. In using wish, you don't have to have it simulate true polymorph, you just simply wish yourself to be a gold dragon. There is no worrying about concentration.
The DM has way too much latitude for that to be a reliable strategy (including going so far as to be allowed to say "no" and fizzling your spell.) And if it does work, you're now stuck as a dragon. Without your class features. While being a dragon is interesting, you're going to have a hard time fitting in with your party again.