in general giant breeds like masitfs and bernese mountain dogs and st. bernards ect are known for their shorter lifespans, however just because the average is 7 years doesnt mean your berner will only have that.
however it DOES make it the absoloute mostofimportance to find a breeder with long lived healthy lines who do all the health checks and knows their dogs extreemly well, knowing the age of death of not only 2 generations but even further back, genetic problems, cancers ect.
the average lifespan for a dan is 701o yrs, i had a dane who was 13 when he passed, remember that average includeds the badly bred, puppymill pups, backyard bred dogs, and dogs that might not have been spay/neutered (which of course increasesrisk of reproductive cancers)
they are a WONDERFULL breed, they love their family and can be protective (especially of their kids) and they love to work, ive yet to meet a berner that doesnt excell at saluking and carting. like all heavy coated breeds most dont enjoy hot weather but LOVE the snow. most berners ive ever met also love to swim. they shed their coatlike crazy and are clumsy pups but supercute.
socilization and at the least basic obedience is a must.
these are BIG strong dogs, so manners are a very important thing to train in from a young age.