BOSTON  Standing in front of his tiny locker in the Red Sox’ clubhouse, Daniel Nava pulled out his wallet and offered a reporter an old driver’s license  one he has held on to since he was a sophomore in high school.

The license listed Nava at 5 feet 1 inch and 105 pounds, dimensions that were the product of careful strategizing by Nava, who for years had aspired to break the 100-pound threshold.

“I rounded all my numbers up,” he said late last week. “If I put 100, people would be like, ‘You’re 95.’ But if I put 105, then they would be like, ‘You’re 100.’ How about that  three digits right there!”

Nava, who as a call-up at age 27 has been an unlikely spark plug in the Red Sox’ injury-stricken lineup this season, needs no reminder that he did not always seem destined to be a major league player. But if he wanted one, he could just look at that license  or at his unlikely baseball ascension.