I've had a i7 2012 13inch cMBP for nearly 4 years. Still acts and looks like new, I added a SSD a few years ago and I reckon I can get another 5 years maybe more out of it for browsing, Pages etc.
Likely even longer than what some of the members have been posting. I know someone with a 2007 MacBook Pro Santa Rosa chipset 2.4GHz Core 2 Duo with first generation LED backlit display. It is still going strong, though I upgraded it to 4GB RAM and a 1TB SSD. I'm typing this on a 2010 i7 MacBook Pro and it runs fine too! I'd say if you are a power user who uses their MacBook Pro for business, 5-6 years, if you do light stuff with it it can easily last 10 years with maintenance.
my
2007 macbook pro 15'' lasted 6 years till I sold it.
2008 macbook still going strong
2008 black book still going strong
2011 15'' macbook pro still going strong
just picked up a 2016 macbook pro 13''
my older macs, i give to family members in-laws w.e