I feel age is a non-factor with things like this. I believe maturity is most important. If the child is big enough to safely use the stove and has shown me that they are responsible, then that is the right age. Perhaps I'm slighted by the belief that exposure and explanation prevent accidents. Teaching our children the right way to handle potentially dangerous things satisfies their curiosity in a way that keeps them from trying to do so without us.
i.e. - When my children wanted to climb the stairs, I didn't tell them no. I showed them how to do it properly (all 4's up, butt coming down) figuring I wouldn't be able to be over them every second of every day. This gave me the comfort to think if they escaped my sight, perhaps they would be better skilled at the activity thus decreasing the chance of falling. They also didn't seem as thrilled by the idea since I allowed it. Not much has changed over 15 years. :-)