Depends on what he's fighting.
Articuno: Yes, easily. Articuno's massive Special Defense still isn't enough to defend against Flamethrower more than maybe once. Plus, Charizard can learn Rock Slide (4x weakness!) and Swords Dance to back it up.
Zapdos: With Rock Slide and Swords Dance both operating, it might work, but if Charizard doesn't have at least one Swords Dance in operation when Zapdos shows up, he's dead.
Moltres: Swords Dance plus 4x effective Rock Slide should do the trick.
Raikou: With Earthquake, Charizard stands a chance, but only if it's already been boosted with Swords Dance.
Entei: A good hit or two with Earthquake ought to obliterate this thing, and it won't be able to fight back very well.
Suicune: No way. It's got the elemental advantage and its defenses are too high to kill it before it kills Charizard.
Regirock: Charizard has a 4x weakness to Rock and no real way to fight back with that insanely high Defense. Ouch.
Regice: Charizard could beat this one. Though its Special Defense cancels out Flamethrower's advantage, it still can't withstand Charizard's physical assault, especially not after Swords Dance is brought into play.
Registeel: Insanely high defenses, but this time both Flamethrower and Earthquake are super-effective. Toss on a couple Swords Dances to overcome his Defense and Earthquake away!
Among the ubers, most are too strong for Charizard to do much against them, except for Celebi, which gets burned to ashes.