You can never look past Crosby, but I see one similarity but two big differences between these teams.
They are very similar in age up front. The average age of Pittsburgh's 9 oldest forwards and Boston's 9 oldest forwards is practically identical. Both teams carry four forwards age 34 or older. When you get to the 4-5 youngest forwards, the Bruins are a bit younger but also much better players (for example Pasta is among the Bruins 4-5 youngest, as is Zacha and Debrusk). Let's face it, the Penguins have no one like Pasta. An elite forward in his prime. They do not have one of those.
But the Bruins are much younger on D, younger yet still experienced. The Bruins best D-man is actually their youngest (McAvoy). Their two oldest (Forbort and Orlov) are just 31, meanwhile the Penguins could potentially dress five D-men age 32 or older, with the sixth guy being 31. The Penguins two most important D-men are both 35, meanwhile the Bruins two best are both in their prime. I have to think late in games, especially if the series goes a bit long, should favor the Bruins D over the Penguins older group as far as the fatigue factor goes.
At the end of the day, the Bruins have more and better players in that prime 25-31 age range than the Penguins do. I think that's significant.
I think the Bruins have a clear advantage in net and really doesn't require any elaboration.