As with others there are what I now recognise as key points, however I also recognise now I lacked anything in the way of formal rigour in approach compared to what I know now and approaches I take now.
PC stuff sends us back to 286s still being current. Was messing around with the rudiments of electronics back then too (had, still have even, one of those things with components and springs and wires), and lego technic and a toolkit when I was 5 meant I was no stranger to the insides of things and general mechanics.
Had some minor experience with savestates, peek and poke on the commodore 64 but it was more copying things from magazines than knowing precisely what I was doing. Never really did much with the vic20. Programming arguably came with some flavour of basic on a little toy computer thing from vtech more than it did with the C64, and qbasic on the PC (got to love gorillas.bas and nibbles (think snake on a phone).
Amiga was when I first properly noted things (trainers, intros, art/music associated with said same, lingo, copied games, anti piracy...).
Had a few lucky lucky man 30 in 1 things for the gameboy.
Emulation appeared around 1998-2000 for me (in my case disc from a computer fayre with genecyst and a bunch of megadrive games), though PC stuff was also a thing by then (remember some people otherwise important in my formative years downloading Windows ME when that was new).
GB/GBC emulation soon after. Some friends did SNES but I mostly missed out there.
More intro to hacking as well as said fayres also sold discs with all sorts of fun programs, examples of hacked sites and more to look at.
PS1 mod chips and cheat cart along with a burner soon after, and the anti piracy race in that. PC throughout it all too, including pulling apart games to explore their files, settings and the like (though nowhere near as systematically as I can do now). N64 cheat cart taught me to make cheats
and I had a similar thing for the PC (was Datel I think and came with a dongle for the parallel port... I did not know better and that I could have used any number of debuggers for free, though did not really have internet outside of libraries down town and school).
Technically did a light bit of dreamcast (still have the utopia disc my dad got from a friend in the pub) but nothing to really note there.
2003 or just after had messed with a bit of GBA emulation in the years prior but did not have the PC to do it justice and got a GBA flash cart and GBA-SP.
All downhill from there. Stopped being as much of a guide follower to instead go on the path to hack maker and guide writer. Learned the ins and outs of flash carts, emulators, took up ROM hacking in earnest, repeated for the DS, xbox, 360 and yeah. Already had a fair bit of hardware experience from the years prior and had biased my education towards it and continue hardware/electronics, programming and hacking to this day.