The lifespan of a laptop (or any device really) depends on many factors, but if it is well taken care of it could last for many years.
As CWanamaker said, avoid heat if possible and keep it clean. If you do open it to clean it yourself, remember to touch something to release static electricity and if you open laptops or desktops often, they sell bracelets to help with this. Static electricity can destroy it quick.
You also want to keep updated anti-virus software to keep a virus from destroying the lifespan from within.