"Mommy" and "Daddy" okay past what age?

Personally I've always hated hearing someone who is 14 years or older/high school age, using mommy or daddy every time they refer to their parents. Agh and hearing someone 20+ using it, it just doesn't sound right or okay. 
10-13 still bothers me slightly but they can sort of get away with it I guess... :/
But I still think the absolute limit should be 9 or 10. Once your kid gets to 6th grade it should become "Mom and Dad"
This is all just my personal opinion here! Not looking to start anything xD, I'm just curious as to what others think about what age is appropriate to use Mommy and Daddy till.
Thanks! :)

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