Yup tires get hard with age because the tread of a soft tyre changes with the age. The wear and tear of tyres makes it harder with time.
Harder with time does not mean it becomes more hard than lm 702 or other pretty hard tyres. But it means its softness decreases when they become old.
I used advan db for 40k kms and then replace them with new advan db,s. i instantly felt that ride became softer and less noisier. Why did i feel that when tyres were same. ? Got my point
What causes the grip to improve after certain kms ?
Try getting brand new tyres and do hard braking. They wont perfrom. Why because tyres are coated with a special chemical to prolong their shelf life. A few hunded kms are required for a tyre for a proper break in and start performing to its optimal level.
In my experience of using advan db. Advan db performs optimally after 3k kms.
I also used michelin primacy 3 and i felt lack in grip while braking in first 1000 kms. After 1000 kms the grip of tyre increased and braking improved.
See "break in of new tyre" at google