Forgive me, but your father is not a deep thinker.
If glassmaking was done, a piece of glass makes an excellent shaver. I heard that it was used in the old West, but I don't remember my source.
A knife could shave a person, and some people shave with knives from time to time.
Obviously, if you have the technology to make a sword, you can make a shaving instrument.
For the sake of argument, assume your father was correct.
I am sure that if God is bright enough to figure out how to make a Universe, He could tell people how to make a shaving instrument. The fact that He didn't means that beards were no problem for Jehovah.
Jesus supposedly had a beard. Jesus could do miracles. If beards were wrong, why didn't Jesus just miraculously shave himself? Such an ability would be noticed, giving further evidence that Jesus was lead by God.
Richard