Rather than have an interesting question buried in a thread about mayonnaise thought we might as well have a return of gbachef with a thread on it.
To that end what age did you start cooking? No being cute saying baking is not cooking. Unlike many times I will also count putting things in the oven from a pack in the freezer as this.
The answer for this for me... I don't really know. I can point to what age I got a tool kit, though I used the others lying around before then. Cooking though...
I used a table knife to cut up strawberries from when I still needed a step stool to see the counter. Was not a great event moving to proper knives later on, remember peeling (with a knife) and coring cooking apples around 7 but there was probably stuff before then.
I was involved in aspects of cooking early on; mixing things in a bowl, making pastry, kneading bread (plait bread is a favourite to this day), chopping things...
Can't remember the first time I warmed soup or pasta out of a can in a pan (microwaves are something we never really bothered with growing up, and I am not old enough to have been before they were reasonably common or still rich person toys) but it would not have been too much later, doubtless was being watched over though for the first few times. Had gas wherever we were at as well as some seem to find that scary (personally I have more apprehension about electric). Would then have not been notable to be the first loose pasta from a pack (though might have been noodles there), and similarly don't remember the first time I chucked some frozen vegetables in a pan of boiling water.
Would have been a tiny older before I was left to my own devices to cook some meat that might have bothered me had I hosed it up but still south of double digits. Putting chicken breasts with some seasoning in an oven is no different than chucking some breaded or battered freezer fodder in the oven and having that cook though. Recall having to use the step stool and stand by the side because I was not tall enough to get it out of the oven (was halfway up a wall with door opening down rather the floor standing sideways opening I am more used to today. Would not have been much different in age before being guided through steak on the bbq either.
First full meal by me for more than me is going to be similarly blurry; do sandwiches and salad for a lunch count? Bagged salad was not a thing back then and even to this day I don't use it (thus everything would have been peeled and cut), would have mixed up sauces, sliced/grated cheese and sliced the bread for the sandwiches too, before plating and arranging on a table. Pasta and something from a pack in the oven? By and large my parents did most cooking but everybody helped as it were. Other than snacks then never ate in front of the TV or in our own rooms, sat down to something at a table basically every night with whoever was there (late/night shifts and working away troubling things there) and that never stopped.
Ratios, substitutions, dietary fiddling (dairy, eggs, nuts, wheat, meat... it is where the taste is but I can deal with it if I have to), bulking/thinning on the fly because surprise guests, reuse of leftovers, experimentation, equivalents/function reasons for things, making something from whatever was cheap at the (super)market or about to go off, how to pull things back when you screwed up, seasoning... all formed within that too. I got burned, I got sliced, I got abraded, I trapped fingers in things, got sprayed in the eye, unintentionally dyed my clothes, broke things, dropped things and in doing so learned not to do it again.
So yeah the traditional gradual acquisition of skills approach was used for me, and my siblings, starting very early. Probably my mum more than my dad but both cook very well and I certainly picked up a lot from him (meats and sauces more there). Started rather young it seems, and if my experience at university was anything to go by then at least by that point a rarer one (though in retrospect makes sense of some of the more bizarre cooking rules in the handbook there).
As far as the charge of making intricate meals then depends. If you mean the stuff like you might see in food photos then I am still from the UK; everything here is slop and if you make a lasagne, shepherd's pie, curry... that does not look like slop it is because you have no sauce and thus might as well not have bothered and while they say the first bite is with the eyes then much like those that grew up eating smash not liking mashed potato (met that a few times) or only knowing sweetcorn from a pack/tin then a plate of curry is going to get my mouth watering way before two small colourful dollops (drips wiped off of course) of something on a giant plate and an arrangement of sugar lattice work that I have to do a force analysis on to consider deconstructing lest I risk eye damage. There are often a lot of moving parts but that is because it is cheap (more work someone else does, more you pay for the same amount of calories and usually worse it tastes). However laziness also rules the roost here; stir fry is a skill I mastered for a reason, I don't really care for marinading things, the only things that take hours are things I can wander off and leave (or I am making borderline industrial quantities of, mostly to avoid work later). I will put the effort in (or at least more of it) for cake though.
