Is it a natural aging process for women's eyebrows to thin out?

I just turned 60 and my eyebrows are thinner
than they were last year but I still have a thick
head of hair. Is this normal? I thought I read that
if you were having thyroid problems this would
happen so I am confused. I don’t feel bad so I
don’t think I have thyroid problems. I do have
some hair on my chin I deal with. Is this age
appropriate too? Does it go down hill from here?