The tires on my car show none of these signs, in fact, they don't even show much sign of wear at all.
They DO however, need replacement, and they have lost a lot of grip.
Why?
They are too old.
What is the maximum legal length of time that a tire can be used on a car?
I think that this may be a problem for a lot of classic car owners, where the car is driven, but not often enough to wear the tires out.
Between 5-6 years old is when you should look at changing your tyres. After that and they'll be hard and grip will be significantly affected. In Victoria there's no requirement to have tyres changed after a certain year but if they're showing significant age cracks then they must be replaced (apparent defects that may make it unsafe - RSVR 2009).
Often these types of cracks don't appear too bad until the tyre is deflated, when they can show up as huge splits in the sidewalls...