I would follow their advice.
I once fitted a 4 year old tire, it was brand new, never been on a bike or out of storage.
It was a rear & could easily spin it up, power slide and lock the wheel on braking.
It was more like plastic than rubber.
I thought if I put some miles on it things would get better, it did not.
I know there is a recommended age for car tires and I would think the same would apply to bikes but I also think bike tires are more important.
You could be putting your life at risk for the price of 2 tires.
I test all my tires for stopping distance, how fast can I get the bike to stop, you could try that with the old tires, then again with the new if you get them, I'm betting there is a huge difference.
Some of the 19 rides in my shed
2014 V2, Snoopy
2009 Wee, Pumbaa the pig
WR450F, The Blue Postie Bike
YZ250N smoker with rego, Stinky.
Yamaha MT09 (FZ09), The Scud missile.
Club Lead not Club Med.
He with the most toys wins.
Out of my depth in a puddle.
Live life on the edge you will see more that way.
Ridding a motorcycle keeps things in balance.
At the end of each trail and at the end of each day history is made.