On Thursday - his 18th birthday - assuming his measurements read the expected 25.8 inches, he will officially be named the world's shortest man.
His family has been campaigning for years to get Thapa the crown, but earlier requests to the Guinness World Records people were rejected because of the possibility he might grow. Up to now he was certified as the shortest male teenager.
Once his measurements are taken three times in the span of 10 hours he is expected to overtake Edward Nino Hernandez of Colombia, who measures a relatively towering 27 inches.
Thapa, who weighs just over 12 pounds, was tiny even at birth, weighing just 1.3 pounds. His father says he has no explanation for why Thapa never grew taller - his younger brother is a normal height for a boy of 13.
Local doctors are also stumped as to what is going on.
Thapa behaves and speaks like a young child and attends kindergarten with children 5 years old.
While his father was excited for Thapa to finally enter the record books, the young man was more focused on his birthday festivities.
"I want a big chocolate cake with red decorations," he said.
Thapa is likely to get the cake and more Thursday when the official announcement is made and a celebration is held in Pokhara, a resort town 125 miles west of Katmandu.
Thapa - who already travels as part of a dancing troupe when he isn't helping out his parents in their fruit shop - seems ready for the media spotlight that will accompany his new title.
Next year he is to serve as a government-appointed goodwill ambassador as his nation celebrates Visit Nepal Year.
"I am very happy and excited," he said.