GAH! Dammit, another error! I need to eat more, or sleep more or... something. 
Yes, I'm aware that the phrase Teenager, the word being made of nothing but prefixes and suffixes, the prefix "Teen" being derived from the suffix on the 6 numbers in which Teen is used, and ager, a suffix meaning "of age", I think... IDK been too long since English Class.
Anyway, since we are NOT of age, and scientific studies have shown that we are not fully matured, physically or mentally, it's not quite proper to call us "Immature", as it is in our nature of being to be so.
Moving on; I"m not even going to try to sound all Mr.-Smarty-Pants on this one, I'm just gonna say that the only reason I can see someone being anorexic is as a result of pressures from society; yes this can be classified as an overeaction, however the initial reaction would not have occured if society hadn't placed the pressure in the first place, rather like stepping on balloons of various levels of inflation, some squish, some pop, others go BOOOM! and scare the neighbors. (Wow... I REALLY need to start being more healthy if I'm devolving into anologies like that)
As for the other addictive habits: I will agree, most addictive habits (that do not include addictants, like nicotine) are a result of the person w/ the habit escaping from pressure or a bad situation by losing themselves within the habit, be it bad or good. A development of a Bad Habit is natural, and IMO, it's a little perfectionist if you're calling someone immature for having a Bad Habit. Chewing nails, for example, can be related to being a pot addict, as they are both addictive Habits.
Banned because I'm not gone yet; I'll be on until I finish Ep. 13 of Claymore.
Richter {^}