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.
As for the Hajj performed by your father while he was young, if it was before he reached puberty, then it did not suffice him from the obligatory Islamic Hajj even if it had been performed according to all its conditions. But if he performed Hajj after he had reached puberty, then that Hajj sufficed him from the mandatory Islamic Hajj even if he was under the age of 15 years old.
On the other hand, if a person desires to pay someone to perform Hajj on behalf of his father or any other relative, he can do so and he does not have to have performed Hajj for himself. However, the person he hired must have performed Hajj for himself. This is the most preponderant opinion in this matter.
So, if the person you hired to perform Hajj on behalf of your father had already performed Hajj for himself, then his Hajj on behalf of your father is valid. But if this person had not performed Hajj for himself, and he performed it on behalf of your father, then the Hajj you financed on behalf of your father is not valid.
You can perform Hajj on behalf of your father if this was mandatory on him if he had not fulfilled it before he died.
Also, know that performing the Hajj is only mandatory upon those who are able to perform it physically and financially (and are pubescent, sane, etc.). If not, there is no sin upon them.
Allah knows best.