There are only conditions that lead to a tree dying young, but you'll notice that even something as small as a rose bush can last through generations if well taken care of. This is not to imply that your parents have done anything to "kill" their tree but with the wishy-washy weather we've been having don't be surprised if the plants in your landscape aren't doing well.
Depending on the kind of tree they had, and their location, it could really be a number of issues but to answer your question, no most trees don't have less than a span of twenty-five years unless stunted in some ways. Make sure they are not fruiting trees though, because those could become easily infested due to pests and what not.
Do your parents a favor and look into the type of soil they have. If it's muddy soil, it can actually keep the tree from being able to root itself properly, as well as acquire the proper amount of water. Also, make sure the tree is suitable for the region your parents live in. Also look into termites and the type of mulch used.