In his previous two NHL postseasons, Tyler Seguin was still just the new kid, a young man with tremendous potential and a lot to learn about life, on and off the ice, in the big leagues. Come playoff time, any good hockey person knew better than to expect too much from a youngster like Seguin. It wouldn’t be fair or reasonable to ask a teenager to step up and deliver amid the heightened intensity and pressure of the playoffs. But Seguin’s status has changed as the Bruins face off tonight against the Toronto Maple Leafs in Game 1 of their Eastern Conference quarterfinal series at the Garden. He’s not the young, raw kid anymore — even if he is just two months past his 21st birthday — but a player the B’s desperately need to be very good. In recent Bruins-Maple Leafs matchups, there’s been so much pressure on Toronto winger Phil Kessel; now he’s got company in that regard, as a major spotlight will be focused on Seguin. In the 2011 playoffs, capping his rookie season, Seguin was a healthy scratch in the first two rounds. He was forced into the lineup at the start of the conference finals vs. the Tampa Bay Lightning by Patrice Bergeron’s minor concussion, and responded with a goal and assist in his first game. Seguin then added two goals and two assists in his second game. Seguin’s contributions had a profound impact on the 2011 playoff run. Indeed, it could be argued that there would have been no Stanley Cup but for what the then-19-year-old was able to do. It was an unexpected delight for the team, a bonus. This time around, the B’s need that sort of thing from Seguin — and more of it. There was no pressure on him to produce back then. Now, with 20 playoff games (five goals, five assists) on his resume, there’s plenty of pressure. “I think Tyler understands that,” Bruins president Cam Neely said as he watched practice yesterday at the Garden. “This is a couple of years removed from when he stepped into the playoffs against Tampa and had that great game for us. I know that he likes to be counted on and relied upon. It’s really going to be up to him to show what he can do. He’s got the skill set for it, and he’s got the experience of what it is to play NHL playoff hockey.”