There are many products available to purchase that contain a variety of minerals and vitamins. Because the needs and weight of teenagers differ from say, five-year olds and men from women, young from old, well to infirm, suppliers make many choices available to try and cover the whole market.
Your choice of Teen Vitality may still be suitable for you to take as it is a vitamin supplement. Provided you do not suffer in terms of the warnings on the package insert (for example, pregnant, etc), the age specified means that the product is designed for teenagers in that age bracket therefore may be less than the recommended daily allowance (RDA) for a twenty-year old.
Any of these over-the-counter products are manufactured for an "average" individual within the specified gender and age range. Vitamins and minerals often need to be replenished daily - whether you choose to do so through your diet or supplementation - and therefore you may take this product knowing there may be RDA deficiencies.
When deciding a question on health like this one, it is essential to confer with your professional health care provider.