For the category of this sub-forum, my two MacBook Pros are 9 and 7 years old.
An 'ordered-the-day-the-Intel-releases-were-announced' first-gen early 2006 MacBook Pro (ordered the highest-spec model the ordering system would let me order - they later bumped the CPU speeds before shipping, and added an even faster CTO option, I got the auto-bumped CPU speed, but didn't add-on the CTO faster model.) It's the 32-bit-only Core Duo, so it's stuck on OS X 10.6.
A little over a year ago, I traded my also-ordered-the-day-it-was-announced original MacBook for a 2008 MacBook Pro, so I'd have a portable that could run the latest OS. Still my newest laptop. (My wife has a 2014 MacBook Air.)
Wandering out of the category of this sub-forum; My primary day-to-day machine is a 2007 (first-generation Aluminum) iMac, with quite a few upgrades.
Going
way outside the category of this sub-forum, my oldest Mac is an original 128k Macintosh, with a serial number indicating it was manufactured the last week of 1983.
Just bought a minty Late-2014 rMBP...and I'm keeping it until "the wheels fall off"!!
Obviously, that's my philosophy as well. I use a system until it can no longer meet my needs - usually due to the hardware no longer supporting the current OS.