Nehru became Congress president in 1929 at the age of 40, Indira in 1959 at the age of 41 and Rajiv Gandhi became party president and prime minister when he was just 40. At 43, Rahul Gandhi takes over the mantle of the party as vice president, while his mother continues to be president.
In 1959, Indira was just another party president and her actual takeover bid started in 1963 with the Kamaraj Plan that she schemed with the veteran from Tamil Nadu. She convinced her father that it was time for the younger generation to take over from the old guard. But soon after the Kamaraj Plan, Nehru died, not allowing Indira enough time to gain grip.
After she became prime minister in 1966, she fell out with Kamaraj, who too joined the old guard to corner her. In 1969, she confronted the old guard upfront and captured the party under her tight authoritarian grip. In all, it took her 10 years of bitter battles.
Rajiv Gandhi was more unfortunate and untactful. Circumstances following the assassination of Indira Gandhi in 1984 sprung him into the leadership unplanned. His going as the general secretary of the party was hardly reassuring - his public humiliation of the Congress chief minister of Andhra Pradesh had triggered the birth of Telugu Desam. Within a year of taking over, Rajiv declared a war on the old guard whom he termed "power brokers." They soon ganged up to entangle him in the Bofors scandal while his own handpicked set of new leaders failed him miserably.
Both Rahul Gandhi and Sonia Gandhi are mindful of this Congress minefield - the reason why the young Gandhi reassured the old guard repeatedly that they will have a place in his scheme of things. He has the luxury of trial and error as Sonia's authority over the party remains absolute.