I think Stig started a thread about this, recently. Asking if anyone had ever had an 'age related' tire failure. I think the answer for most is no, we've never had an age related failure. But why chance it on a 2 wheeled vehicle where your life may depend on your tires?
Will they fail? Probably not...but maybe? So why take a chance...replace them!
I have older tires on my scoot, 2014 and 2015. Planning on swapping them out this year even though they have virtually no miles on them.