A friend of mine just now did the quest that spawns random dragons and he's 98 hours into the game. It was a good 30 hours before I started seeing random dragons. I'm currently playing with a new character and will probably wait quite a while before I start fighting dragons. How long have you guys waited before allowing random dragons to start showing up?

whenever you feel like it realy, my newest character is at level 59 right now and i havnt start the whole dragon thing yet the last few times i did they always seems to end up eating the shopkeepers leaving me with a larger amount of junk

If you never do the quest for getting the dragon-stone, you will never see dragons until then.