My kerosene heater is 15 years old. I have used it maybe 5 times, for an
average of 4 days each, over those years.

I have never drained it, and it works fine. I have also used 8 year old
kerosene, and it burned perfectly well. So, unless someone can document the
deterioration that occurs in 6 month old kerosene, I will have to think it
is doesn't happen. Gasoline gums up and the high volatiles evaporate; that
can't happen to kerosene.

On the other hand, I have refueled while it was burning; and I have to
concede that is pretty stupid.