All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
A father is responsible to spend on his children on two conditions:
a) While they are needy and cannot earn money. If a child has sufficient money to fulfill his needs, or if he is able to earn money, then the father is not obliged to spend on him.
b) The father has money exceeding what he spends on himself and his wife. If he does not have any money after fulfilling his necessary expenditures, then he is no longer responsible to spend on his children. The Prophet said: “Start with your own self and spend on yourself; if anything is left, it should be spent on your family, and if anything is left (after meeting the needs of family), it should be spent on relatives.” [Muslim]
In another narration, the Prophet said: “And begin (spending) on the members of your household.” [Muslim]
However, you should refer to the Sharee'ah courts since the age and the amount of maintenance is determined through them, and one is obliged to follow their rulings.
Allah knows best.