Is it normal or even helpful for teenagers to still be eating flintstone vitamins?

Yes: It is normal and somewhat helpful for teenagers to take a daily multivitamin. Teens often don't get enough vitamin d or calcium in their diets. If they are choosy eaters and don't eat a variety of foods, they may be low in other vitamins. A teen is usually big enough to take an "adult" multivitamin, but it is fine for him to take several kid's chewables instead (but he'll be chewing more sugar).

Need for vitamins: If adequate diet vitamins are not needed. If not complete diet there are chewable vitamins for teens and adults