What age does a child be petitioned by his father in the US?

Answer 1

To answer the question, the Immigration status of the petitioning father has to be clarified.

For US Citizen Father or Parent

The father can petition the child of any age. The age matters only on how fast the visa can be processed. For a child of a US citizen father, the child who is below 21 years old and is unmarried will not be subjected to numerical restrictions as to waiting time for a visa to be available. Processing time from petition could take a year or less.

For a child over 21, unmarried, the waiting period depends on the priority dates being processed in the first preference category.

For a child who is married regardless of the age, the waiting period depends on priority being processed in this third reference category.

For an Immigrant or Permanent Resident Father or Parent

The immigrant father can petition the child regardless of age as long as the child is unmarried.

The children who is below 21 waits as long as four years to get the visa or depending upon the priority dates being processed.

The children who is 21 or over waits at least 10 yearsto get the visa or depending upon the priority dates being processed.

For reference try checking ins.gov.