Thinking that gambling mistakes can be done by only teenage gamblers or newbies will be a misconception as this is applicable to all regardless of the experience or the number of years you have spent gambling even if you may want to consider yourself a professional, you are prone to make gambling mistakes and interestingly you may never get to out grow it.
But then teenage gambling is something that I feel should be discouraged totally as it doesn't make any sense, this is because most teenagers are yet to be able to take sound decisions for them self and be able to face the consequences regardless of the outcome. That's why every gambling sites usually have a certain age they dim fit to gamble as by that age it's expected these gambles know what they are doing.
Most countries and gambling sites have legal age they allow to gamble as this said age is expected to be an adult and probably have some level of self dependency and not the ones who are still dependent on parents or guardians. As the ones who are still very much dependent (teenagers) don't have a means of income and may want to engage in unhealthy habits to raise funds to fund their gambling habit.