WOW! I haven't seen this many wrong answers all in one place in quite a long time!
First of all, as one person pointed out, it depends on which country you live in on this very big planet.
More importantly, in MY country, (the USA), a minor CAN win the lottery if he is given the ticket as a gift. If he is the sole owner of the ticket, then the prize must be cashed by a guardian and put into a Trust. I imagine the same would be true if he were a part of a group. That portion of the prize would have to be put into a Trust.
With all that said and done, it's a bit odd to say that a 17 and 15 year old were actually part of a group, yet they can still claim the ticket was given to them as a gift. It might be hard to believe. If you're part of a lottery group, then that does not imply receiving a gift. That implies intent to gamble as part of a group. It could get hairy.
Even if it is 100% legal, shame on these people for allowing a 17 and 15 year old to play. It's a HORRIBLE precedent to set, and a horrible example to set for minors. Teens are very impressionable. They should NOT be encouraged to gamble in any manner.