Building on b_jonas' answer, one of the reasons for a wizard's life being so extended is definitely because of their magical remedies for problems that muggles do not have access to. I would not necessarily expect that wizarding blood would have an impact on one's lifespan, as when considering the respective wizarding skills of Hermione and Ron, Hermione, the muggle-born, is much better. Hence, I would agree with b_jonas in that it's the magical healing remedies.
Now, I would argue that the lifespan of squibs has slowly increased with the attitudes towards squibs increasing after the release of the book My Life as a Squib by Angus Buchanan in 1900, which has been very popular. However, according to this article on Squibs, they still aren't quite accepted into the wizarding community wholeheartedly. Hence, my final answer would be that it depends on their involvement in the wizarding world. Those who choose to live in the muggle world would have a normal life (by muggle standards), but those who dabble with or live in the wizarding world would have a slighly longer lifespan than the average muggle. Bear in mind that they may have second-class treatment for illnesses/ailments because of their status, so I wouldn't expect them to live as long as a typical wizard.
See this question on the average lifespan of wizards as well.