o...that's very good question.
Personaly i think 18+age is good for sfi because...
1.sfi is future way for earning so at 18 way get full advantage for earning.
2.sfi is based on learning at 18 learning is easier compare to other ages.
3.at 18 we are confused what i do for earning so online income like sfi is excelent choice.
4.sfi make our future better in 18+ way have a chance for good future and for also our for next generation.
5.18+ is very confused age specialy for earning money sfi give the chance to earn money without a wrong path so,i personaly recomeonded 18+ to join sfi without going on wrong path and make some money and have a good future.