is it possible to defeat the dragon
Very Possible, you just need enough status.
In order to produce the status necessary to defeat almost anything in this game. You need to gain access to the extra dungeon.
On the extra dungeon at the last floor there is a set of bosses in which you can probably manage to defeat at level 150+ or so during your first run of the extra dungeon.. by then you would have enough G already to buy tonics.
There is a shop on the extra dungeon that sells these 2.0 Tonics. Which gives about 250 HP/Mana or 25 of which ever stat you wish. I personally prefer Magic as one spell "Thor's Hammer" Paralyzes even the last boss.
To earn gold easily for this you need to constantly trade levels to Mazenda. Each time you trade levels to mazenda the reward she gives you also increases.. If you trade 99 levels to her you can get about 500k G. This stacks everytime.. with the extra dungeon last floor you can easily get to level 99 in a matter of 3mins or about 2 runs of the last floor alone. Repeat this process of trading levels to mazenda and soon the income will be sufficient to buy practically anything. Particularly those stats.