My husband is the same age and had removal(may be partial) when he was 6 years old
because he was over active. He does well on Armour thyroid but not on any synthetics. I put 1 drop alternating with 2 drops in his coffee, the same with liquid selenium. Once I raised to 3 or 4 drops,since they were testing him every month and he became hyper, so now I stay under 2. If you father goes for regular tests you should not have a problem, we don't tell the MD what we are doing.
BTW our insurance does not pay for Armour but it is not very expensive so we pay for it.