Name change for this post so that I don't accidentally out myself. Unusually, for once I haven't read the whole thread before commenting so I'm very happy to be shot down in flames or accused of not reflecting / acknowledging earlier comments.
I've often seen class defined by your father's occupation at the age of 12, which is sexist but certainly works in my case. Certainly more reliable than a recent predilection for avocados or whatever, I suspect?
Dad left school with no qualifications to work at the local coal mine at 14 (not initially underground, although that soon followed). He later succeeded in escaping what seemed to be the predetermined fate of a working class boy growing up in his particular Midlands town and instead achieved his aspiration of becoming an actor, notwithstanding a brief interruption when he was called up to do his two years National Service.
For the first five years of my life our family lived in a "static caravan/mobile home", in part because Dad couldn't get a mortgage due to the insecurity of his occupation. (As it happens, it took some serious persuasion by my mother to get "Actor" recorded as his profession on my birth certificate. I should mention that she was carving out her own career but temporarily gave it up when I and my sibling were born. If it wasn't for her efforts and sacrifices none of what I'm mentioning would have been possible, so I'm certainly not trying to underestimate the role she played in all of this.)
By my early teens, Dad was an actor with the RSC so, in my opinion, although we were far from being well off it would be somewhat disingenuous of me to claim to be working class, despite my early childhood experience of poverty.
FWIW, dad's career wasn't "successful" as is perhaps conventionally judged in terms of the acting world. (He most definitely isn't a household name, although he inevitably worked with many who are.) But he spent a lifetime earning a living in a profession with an 85% unemployment rate (and where the 15% who are in employment are very often the same people), which is an achievement that shouldn't be lightly dismissed. He is still with us, although sadly he remembers very little these days - he, Mum, and the rest of the family who live nearby will be going out for lunch on Father's Day on Sunday.