I’m 63, and I never had mumps, measles, or chickenpox... and when my younger half-sister had measles I was at her side, trying to get them next.
I tried, I really did. I took care of her, fed her, put her fork and spoon in my mouth after hers and I read to her, just stayed right there. It was a chance to stay home from school so I was in.
The doctor told my mom it was maybe because my normal body temp ran a little high (above 99), and maybe the germs just hot killed off before they could take hold? Whatever it was... I never got them, even when I was visiting friends and their little boy was feeling ignored and I had him on my lap reading his favorite book to him... then when he was called in to eat and how to bed, his mom came out to say she hoped we had all had chicken pox because when she had dressed him for bed he was covered, and had a mild fever.
Still, nothing. So whether I was consciously trying or just accidentally exposes, I couldn’t seem to catch a childhood disease. And I’ve been warned that these can be particularly dangerous for adults, more so the older you get.