Is there a socially acceptable calf width when deciding if you can wear a kilt or not ?

Nope. Some American Kilt makers for men even make special kilts for really fat guys, not just overweight, but three or four feet wide.

No. Kilts are either used as girls's school uniforms or Men's traditional highland dress. Prince Philip is a million years old and still can be spotted in Highland dress. Highland dress tends to look better on men who are robust and athletic but there aren't any rules per se.