I don't. I have met the most immature and childish people in their 30's and beyond but at the same time, met some teens who acted more like adults than their parents. I feel like age is just a number (when it comes to maturity of the mind) and the average 18 year old is far from an "adult". If we are talking purely on physical form, yes I can see age being a factor but as far as actions, thinking, and how people generally are... I don't factor in age.