Normal flaking for tyres reaching the remaining half of their life.

Just reconfirm with the tread wear indicator (go along the line where the little triangle is).

Technically, can last until the tread and the bump are same height. but when the difference not so obvious, should be about time to change. If more than 4 years, just change it because it has hardened noticeably compared to new under our climate.

How much mileage you've put on under this set of tyres?

After these many mileage, just get it changed.

The price adjustment due to re implementation of SST is going to bring tyre prices up. Although by right, only NEW supplies at/after 1st September should be affected, but knowing how unscrupulous most of the businesses here, they will raise prices exactly at 1st September despite selling existing stock.