Actually, that kind of continuation isn’t ideal. Discourse tracks solutions to problems, which is both reflected in topic status and helps increase user standing of whomever solved the topic. There can be only one solution per topic. To not undermine that system it’s best to stick to one topic per problem, even if it’s a “me too” (especially since quite often a problem that’s perceived as the same by original poster is in fact different). And for that reason it may indeed be helpful to auto-close support topics after a certain amount of time (although a year is probably too much).
Outside of support though, I don’t think there can be any universal rule. If someone decides to comment on a two-year-old artwork (thus potentially exposing it for other users who missed it), or update their sketchbook after a hiatus, or continue talking about whatever in Off-Topic Chat - so long as discussion stays relevant, I can’t see why that should require starting a new topic.