We know that Wizards and Witches have a prolonged lifespan, but we also know that a Squib is someone born into a wizarding family who doesn't have any magical abilities.
But does this mean that they no longer have a prolonged lifespan? or is it that their families' blood is what causes their longevity?
I know that Filch is a Squib, but I don't remember any mention of his age.
In-canon, there are no known squibs that have lived beyond a normal human lifespan;
Angus Buchanan died at the age of 80, Marius Black died age 80(ish). Argus Filch is approximately 60-70 by the events of Deathly Hallows and Arabella Fig is probably around 70.
I've been unable to locate any canon description of the longevity of a squib (either in the books or interviews with JKR) but given that known squibs have died of non-violent causes at around 70-80 years of age, this would strongly suggest that their lifespans are similar to those of muggles, despite having access to wizard medicines and medical treatment.
Speaking of Filch, there's no canon mention of his age but we can take a few educated guesses. We know that he came to work at Hogwarts in 1973 and it's likely that he was at least 30 years of age when he took up the post of caretaker (given the level of responsibility that the position entails) which places his birth-date neatly around 1940-1945. The Harry Potter Wikia describes him as being "around 65" which tallies nicely with the out-of-universe decision to have him played by (70 year old) David Bradley.
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.
