Bike age

You have to be a bit careful due to the progression of standards, but 2014 shouldn't be too bad.

Things to avoid:
26 inch wheels (harder to find new tyres, eventually harder to find parts)
Quick release axles
Weird steerer tubes standards
Proprietary parts (e.g. specialised/scott shocks)

Things that will make it easier to replace parts:
Boost wheels (unlikely in 2014)
Brakes from shimano or sram (might be harder to find pads for older/exotic brands)

You may want to size up to be closer to modern geometry (bikes get a bit longer every year, most people like the longer bikes).

You should also do a quick check to see if that particular model had issues that year. This used to be a much bigger deal, as many brands were known for welds that cracked, but i think this is mostly a pre-2010 issue largely resolved by 2014.

But I would question if it make sense to buy 5 years old bike. What is the deal? What model we talk about? With a lot of direct sales brands and more companies on the market, one can buy an amazing bike for good price these days...

Biggest problem would be wear parts such as seals and oil.
So you should probably factor in a possible service on suspension and brakes.

Other than that, 2014 isn´t too old and should be fine in terms of geometry.
Contrary to popular believer even 26" isn´t a problem, given that a lot of manufacturers still release new components, especially tires, in 26" and even if not, old standards like the Minion or Magic Mary are still available. So no real problem there IF the price really is that good.
Maybe just show us the bike or tell us exactly what we´re talking about so we can tell you more.