Evidence for use of fire in general seems to go back about a half million
years or so.  Clear evidence of use of fire for cooking is much more
sketchy.  I for one find it absolutely impossible to believe it would take
hundreds of thousands of years for anyone to think to put a hunk of meat on
a stick over a fire.  Humans have a weird fascination with fire as it is
(we're the only animal that does, apparently) and we like to stick things
in fires.

No way to prove it of course, so maybe I'm wrong, but I find it thouroughly
unbelievable that we would have fire for half a million years before we got
around to tasting what it did to our food.

As for lifespan: I stand corrected.  It is an item of debate.  What we know
is that people's lifespan dropped when they adapted to agriculture and
started eating a lot more grains and such.   Beyond that, so far as I know
there is no evidence to suggest that humans suddenly became shorter lived
at some point earlier for some inexplecable reason.

Cooking food has its drawbacks but it has its plusses.  It may add some
carcinogens but it also eliminates some.  Some experiments have shown that
meat cooked over an open fire is actually protective against cancer (I'l
find a reference for that if challenged, it's been a while but I can dig it
up, it was an Australian study).  And of course if you cook fire you can
eliminate some of the diseases that meat carries.  Therefore it's as likely
to have conferred survival advantage as the opposite.

Then again, there are clear accounts of hunter/gatherers eating parts of
animals raw, and of course eating raw fruit, nuts, etc.  I don't mean to
suggest everything or even the majority of foods should be cooked.