Am in tittle to pay child support to a grown adult

First its not a good idea to piggyback your question on another thread. This can lead to confusion. So I've moved your question to its own thread.

First by definition an adult is grown so the phrase "grown adult" is redundant. Second, did you mean entitled?

You can pay support to anyone you want. But an adult child is not generally entitled to seek support. Support is paid to the custodial parent or guardian before the child reaches adulthood.

Where is this happening at? In general most states (U.S.) have an upper limit on child support. The only time that limit is exceeded is in cases of agreement (both parties agreed and signed by a court) or if the custodial parent applies for child support beyond the given limit due to medical reasons. Some children require a lifetime of support.