Assuming the laptop does not get outdated after six months, I think five years is a reasonable life expectancy for an everyday laptop. If you do intense processing or gaming it would probably be shorter.
I think 5.5 years of a Vaio is great. My Vaio lasted about four years before the CD drive broke, some keys became sporadically unresponsive, and the screen started to flicker when I try to adjust the screen angle.