BOSTON — While Tom Brady’s age gets most of the attention when talking about senior Boston athletes, Zdeno Chara isn’t exactly a spring chicken himself. The Boston Bruins defenseman is 41 years old and will turn 42 next month. Chara still shoulders a huge load and skates on the top pairing, regardless of who the mate is to his right. But the reality is, and it’s to no fault or lack of preparation of his own, but Chara isn’t the perennial Norris Trophy contender he once was. And with the Bruins needing him to be at his best down the stretch, head coach Bruce Cassidy was asked after Tuesday’s 3-1 win over the New