My depression came with puberty really - I guess that was somewhat the catalyst.
I first remember wondering whether I have depression, or whether how I was feeling was simply natural and part of life's ups and downs, aged 15. I'm 20 now.
I've pretty much become increasingly depressed each year. It got very severe at 18ish. I have perhaps never struggled more with depression than I did at 18 - not because my depression has lessened now, rather just that I am more accustomed/adjusted to it. I think I probably feel more constantly depressed aged 20, but I am less often completely overwhelmed/bed-ridden by my depression now.
Suicidal ideation probably started lightly/passively at around 16, again increasing dramatically each year. At 18 I was thinking about it a lot, wishing to be dead, but not very actively suicidal. For much of being 19, I felt actively suicidal, but lacked information on how to ctb. I would go to train tracks and stuff, or try and research where I could jump from and how I might get there. These methods are ofc not advisable. Shortly before turning 20, I read the PPHB, and soon after found SS.
That's 4 years of feeling suicidal, and for at least the last 2+ years, I have thought about suicide literally every day. Often, that would used to just mean thinking about in passing, maybe a few times a day. It's obviously much more severe than that now.