>> I can choose for example only to make the bet for one month price for the security I choose?
The above is correct.
For every prediction, you'll be able to select the time you want to predict for, from a restricted list: something like 1 week, 2 weeks, 4 weeks, 8 weeks, 16 weeks, etc. This slight restriction is to ensure that the bets are evenly distributed over time, so we can draw a smooth graph of projected price over the next few months, and compare it with reality later.
>> So if someone is not 21 years old, and not the minor too, they can
>> play because no real money can be the reward? Not gambling.
Yes.