WHY PROTOCOL DROIDS (and Threepio) ALL LOOK THE SAME:
Different interiors, same exteriors. Like iMacs, droids’ shells are interchangeable. Some random shmoe came across Threepio and decided to give him some clothes.
WHY OBI-WAN SAID HE WAS TRAINED BY YODA:
He was. Duh. Obi-wan was apprenticed to Qui-Gon only for the final parts of his training, but when he was younger, Obi-Wan was trained by Yoda. And besides, it wouldn’t do any good to tell Luke about Qui-Gon, since Qui-Gon was already dead, and thus, of no help.
WHY THREEPIO THINKS HE’S 112 YEARS OLD:
He’s got the same processor, but a different hard drive. Perhaps, whoever came along and “clothed” him, installed etiquette and protocol software, which came along with an “Age/Experience” shareware demo… absolutely free!