I would say it's unnecessary to tell anyone. Your dad has survived to the age of 70, no doubt creating his own strategies as he goes along, and I find in my experience the older generation is often very wary of labels that weren't around in their day (my dad is still getting his head around the Asperger label for me, and prefers to call me eccentric, because he says that's how people like me used to be described).
I'm sure my grandad had Aspergers, but I never told him, because it wouldn't have enhanced his life. He'd learnt his own ways of dealing with life. I have mentioned it to one of my sisters, but only because that sister is very open to understanding Aspergers, and it was just a topic of interest. There was no necessity for me to tell anyone.
Is there a particular reason why you think it would be helpful to tell people? If I were you, I would think about what result I am hoping for and how realistic it is that I will achieve this result by telling people.
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'If the shoe doesn't fit, must we change the foot?' Gloria Steinem