Ponting started declining after 2008, Dhoni's decline started in 2014, Sachin's decline came very suddenly, and after 2011 WC, he wasn't the same batter, Sanga for some reason kept getting better gradually and was at his best in the last 3-4 years of his international cricket. Aus had all basis covered, Gilchrist, Hayden, McGrath, Martyn, Symonds were brilliant even till the end of their careers and they had upcoming players like Clarke, Hussey(late entry though), Watto and Tait, which is certainly not an average talent pool. I feel, the amount of cricket Kohli has been playing, he might start declining sooner rather than later, and pretty sure, it will start in at maximum 3 years as he's been one of the busiest cricketers in the world.