This age group spend most of their money on clothes. I have found that most parents are making their child's cell phone payments until they are able to work. On average, this age group spends around $300 - $400 a year on clothes, which breaks down to about $5-$8 a week. There will be some additional costs throughout the year, but parents are still paying for food at this age.
Once you have hit that 16th birthday, purchases tend to increase dramatically. Most kids have a job by this age and are purchasing clothes, occasional food, phone costs, movies, dates, social activities and much more. I found the average to be around $1200-$1500 a year. Clothing was still around $400, but social activities sky rocket at this age averaging around $350 just for social activities (mini-golf, movies, concerts, etc.). A lot of teenagers are constantly going to the mall as well, which adds on additional food costs for around $350 for the year. The rest of this balance was spent on phone costs and gas (if they have a vehicle). This will vary of course depending on how social your teen is, but this is a great starting average for you to consider.
With the beginning years of college, this group spends more than the groups before them. On a college forum (College Confidential), many people have said they spent around $3000 for one college year. This cost included food, drinks, bills, clothing cost, and other expenses. Most admitted that they were unaware of what all their money actually went toward. When you are in college usually your budget is a lot tighter, yet you spend a lot more money on food than in any other age bracket. One could have an on-campus meal plan, but after several weeks of that in a row they get burnt out. They spend money off campus for some "real food." None of these cost-estimates deal with books or tuition, since this range is an extreme amount varying from every college. This $3,000 would be spent for people that live on campus. For those that live at home, they will save about an additional $1000 a year from food costs alone. They will spend more money, however, on gas since they drive to school. This will vary of course depending how far away they live.
If this 18-19 year old age group is just working and at home, they tend to spend a lot less than if they are away at school. With some still living at home, they can spend just right around $1500 for clothes, gas, food, activities, and bills. Once they become independent, and move out of the house, their spending costs will increase. The cost will then vary with rent, utility bills, food, etc. This average can be anywhere from $7,000 - $15,000, depending on where they live and how much they make.