Warren & Debbie
By your discription, you've taken very good care of your tires and you have a good history knowledge of them. If they have at least 4/32nds of tread, I'd run 'em. If less, I'd consider it only because WATER is not compressible and with less depth, the tread can't dissipate deeper water fast enough and could cause hydroplaning...or when it rains, I'd SLOW down.
Most truck tires (with some exceptions) carry six to ten radial sidewall plies and the job of keeping air in a tubless radial is that of the tire's inner 'liner', not the sidewall. As far as age goes, yours are within a generally accepted range.
Different people have different risk/benefit tolerances. Mine may be a little higher than some...I also put my children on a big yellow tin box with NO seat belts and with a driver of questionable character...YMMV Bob