I don't know why you'd want to.. but use this kinda scenario:
You: Hey gramps I've just got to fill out this form for your. uhh. life insurance... can you answer some questions?
Gramps: OK
You: Age?
Gramps: 78
You: Weight?
Gramps: 82kg
You: Uhh. *cough* penis size?
Gramps: What?
You: Penis Size
Gramps: 14 inches
You: Great, thanks.. I'll finish the rest of the form later.BYE!