At 38 years old, Koji Uehara is the elder statesman of the 2013 Red Sox. The fact that he has the infectious enthusiasm of a 12-year-old with all the fist pounding, back slaps and yelling he provoked when he entered the dugout after each of his three perfect innings in his first three appearances is one of the biggest reasons why this Red Sox team has made such a positive impression so far this season. The fact that there’s nothing forced about Uehara’s act only makes it that much more appealing. “Yes, I’ve always been like that,’’ Uehara said before last night’s game against the Orioles. “It’s not that I’m trying to pump up the team or anything like that, it’s more emotional. It just comes out naturally.’’ And naturally, the Red Sox could not be more pleased with Uehara, the star of the bullpen and the most pleasant surprise of any offseason pitching pickup. In his three innings of work, Uehara has three strikeouts to go with the zeros in the runs, hits and walks columns. He is getting weak contact (no line drives yet) and is ultra-efficient with his pitches, needing just 26 for the nine outs. That dugout enthusiasm may come naturally, but it is deserved, too. “He’s a very excited guy, full of energy — I think that’s the way he copes with things,’’ said pitching coach Juan Nieves. “That’s a very relaxed inning for a pitching coach. Don’t quote me — I’ve heard other pitching coaches say the same thing. He’s a pleasure to watch.’’ Manager John Farrell was unsure if he was going to use Uehara last night, but he clearly was not afraid to. He has no problem with the way Uehara keeps bringing good cheer into the dugout after every appearance. “He’s had very good success in back-to-back days,’’ Farrell said. “We also have to balance a full year, his age and our desire to go to him frequently because he’s a darn good pitcher.’’