What is the ruling on vowing to fast a month after the condition upon which the vow was made is fulfilled, along with the repeated occurrence of the act for which the vow was made many times?

The vow of a child is not valid because they are not held accountable. If you were an adult at the time of the vow, then this vow of yours is a vow of obstinacy (Nathr Lajaj), and you have the choice either to fulfill it if it is an act of obedience (qurbah), or to expiate it with an oath atonement (kaffarat yamin). The vow does not become binding upon you repeatedly with the repetition of the act it was conditioned upon. Rather, you are only obligated to fast for one month or offer one oath atonement, unless the wording of the vow implied repetition.