hi iwbftblr i am going to yap about when/why i think listers addiction starts because i think about it a lot
cw for disscussions of alcoholism (obviously) but also sa and poverty and basically anything lister goes through at all. bro is living ROUGH
i don't believe that its as simple as hes just got an 'addictive personality' or he has the addiction gene. jimmy himself even says that "before we got famous, lister showed little sign of being into the party lifestyle, beyond being mildly disruptive at school." (pg 79.) so its most likely due to other triggers that his addiction began.
one of the most obvious things that triggers his alcoholism is having access to money after growing up in poverty. also on pg 79 jimmy says "as soon as we started making money, lister's love for the finer things reared its head." growing up in poverty is fucking rough, and lister is still a young teen when they start getting famous, he has no idea how budgeting, savings or credit actually works. its a very typical childish response for him to have. in the scene where they argue in the bathroom lister confirms that he was very close to living on the streets, so of course hes going to be excitable and reckless when he has access to the wild amount of money they get from being famous. and again, lister basically confirms that this wealth is a big trigger for him, drinking and parties for him is just "enjoying having money and being happy." (pg. 141)
as for when that actually starts, isn't the most clear, but you can sort of create a timeline by looking at some of the extra materials like 'the incident on showday' and the wiki pages alice has made !! while the incident doesn't actually have a canon ending, the things we learn about the characters and how the act tells us a little bit more the ark's life pre-iwbft.
starting with 'the incident on showday' lister is 17 and it's very clear that he's already struggling with alcoholism. it's very much passed the 'just social drinking' phase considering he's (very badly) drinking in secret already. also cecily's 'no drinking on show days' rule is already a thing at the point. (this is all on the starting page of the game)
skipping slightly forward, when you get to the part where you're in the supply cupboard with jimmy, and choose to apologise, lister begins to ramble about his alcoholism and reveals quite a bit.
"look, i just... i know this isn't the first time i've done this and i promise... i swear i'll try to sort it out." / "i just... with the drinking... i feel like i can barely control it anymore, i dunno, and i always do it when i don't want to-"
from this we know that lister knows he has an issue, and maybe that he's been trying to deal with it on his own, but it hasn't been working out. either way, at 17, its already an issue that has been going on for a while. which makes me think that it became an addiction when he was either 16 or 17
we know that at these ages he's been through a lot. he was for the first time when he was 16, and i'd say it's implied that it happened again with kevin but thats a whole other conversation. it would have also been around the time that the suitcase incident happened and rowan was ignoring him, so he would've probably felt very lonely, and partied more to try cope with that. these, plus the money are probably the biggest causing factors for his addiction, at least from my interpretation.
also, as for jimmy and rowan not intervening, through iwbft, especially at the start, lister's drinking habits are sort of portrayed as just this quirk of his. though jimmy's attitude towards it gets more serious as the week goes on. jimmy only comes to the realisation that lister is displaying obvious signs of alcoholism for the first time when he finds him in the bathroom. he does attempt to bring this up to lister, but ultimately it is considered and issue for another day, which results in the whole lister almost dying because red flags weren't taken seriously enough thing. again thats probably better for a whole other conversation too.
but anyway, timeline that makes most sense in my head is:
the ark start blowing up + making money -> the record their first album -> lister is assaulted -> album eventually comes out and they're preparing for their first european tour -> lister accidentally outs jimmy -> rowan ignores lister for 2 months, so probably that entire tour -> lister is extremely lonely -> he starts to party more to as a coping mechanism simply because he can -> he learns that if he's ever sad or stressed drinking 'fixes' it -> congrats !! alcoholism achieved !! -> 'the incident on showday' takes place somewhere here
do not try this at home guys