It's definitely a thing, primarily with stimulant abuse. Not sure there's a standard amount of time in which drugs will age you, it depends on a lot of different factors, such as amount of sleep, hydration, nutrition, etc.
I disagree. Plenty of people are able to quit and not be on maintenance. As well, a lot of the rewiring of your endorphin system is totally temporary and gets better the longer you're sober, whereas with things like meth that are directly neurotoxic, your dopamine system can get totally ravaged after long term heavy use, no matter how long you're sober for, life just doesn't have the same spark.