if that was me, i would continue as normal, the tyres are 4 years old, but if they look good, as stated above with no cracks i would have no problem touring on them, but that's just me
When looking at a tire you should not be checking the fact that the SIPES have alot of distance to the top of the tread, your checking for age, compound of tire and any major issues that have happened to the tire in its life.
you need to make love to your tire, run your fingers all the way around the sidewalls feel for the plys as they run down the side of tire you usually have 4 of them that are noticeable in + shape and are due to the manufacturing process but when you find them not in a + or X pattern its a broken ply also check for gashes gouges and blistering,
next check the shoulder what is the angle of wear if its very steep or only low in the inner half of the shoulder your tires have been over and or under inflated while driving,
next check the center part of the tread for damage cracking leaks etc, its very basic to overlook a major issue between the sipes usually starts to dry rot.
Any tire over 3 years old in the united states WILL NOT EVER do better than its first 3 years in grip rolling resistance and tread wear.
the major thing with tires is they require a lot of basic maintenance that is overlooked, if you run low psi for a day you're going to start a small, Very small tread wear for a underinflated condition and you cant overinflate to compensate for it. Once it starts to wear wrong it can never be corrected.
2ndly you can do all this and still ruin your tire with a simple bad balance, the tire should have a static balance done. (car tires are dynamic balance)
*i may be mistaken and motorcycle tires do need dynamic* but i was told that the wheel (rim) is dynamically balance already and the tires are manufactured dynamically also. if you skip this balance or the tire is out of balance you can cause a lot of premature wear making the tire useless, caused by wheel tramp.
last but not least the DOT number usually a 4 digit number stamped or branded on the tire next to 2 groups of 4 numbers
EXAMPLE : (2606) (6234) (1H35)
^DOT
first set of numbers but its usually only one side so check both it may be before the 8 manufacturing numbers or after this i am not 100% certain
but nonetheless this example would be 26 week of 2006 the tire was made now that being said its very old in US standpoint if the tire was never mounted and sat in a warehouse they could NOT sell this as a new tire
again because the us regulation is 3 year or more is OLD i believe the reason is because the US federal testing determines that at 3 years the treads grip is lost significant enough to cause a loss of control on a vehicle with these tires, also something to do with the rubber drying out .
Basicly, just because the "treads" have big deep grooves between them doesn't mean the tire is ok, you need to check all the information available to you and make a sound decision, its comes down to how much $ you got and how much you value yourself and possession
Please be safe if you are not sure about it just tightening it down a bit more is not the best idea know what your doing what it will cause and why it will cause that.
stay safe ride safe
.
