My husband's name is Timothy and he was Timmy to his family until about 10 ago (he's 38!!!) It took dedicated effort on his part to to get his mother/aunts/uncles, etc. to stop calling him Timmy. As a matter of fact, he has a few distant elderly cousins that STILL call him Timmy and his mom slips from time to time. He says he started trying to be Tim in about the 8 grade, but folks weren't hearing it! He says it's hard being a 6 foot 2, 200+ pound black man named Timmy! LOL
He still let's me call him Timmy though!