Your result
Possible
The agreements set the minimum at 18, so this is a matter of waiting rather than of eligibility — you are on the right route, just early.
Worth knowing that the underlying Brazilian regulation allows a férias-trabalho visa from the age of 16, but the bilateral agreements are what actually govern who can apply, and each of those sets 18 as the floor. The agreement is the binding document, so 18 is the real date.
You will keep the eligibility for some years: the upper limit is 30 in most of the agreements, and 34 for South Korea, so there is no rush once you turn 18.
Two things worth doing in the meantime. Check whether your country's agreement sets an annual quota, since some are taken up quickly after opening and the timing within the year then matters. And if the aim is to be in Brazil sooner, study is a residence route with no minimum age of this kind, and it counts as lawful residence.
Tell us your nationality and your age, and we will tell you the exact date you become eligible and whether a quota affects when to apply.