HEROS NEVER AGE. It is a known fast that in Tollywood, actors age but Heros don't. Heros remain heros from decades together. Whereas, actresses move on to playing roles like sister, mother and even grandmother.
With all due respect, let's leave the senior actors like NTR, ANR, Shoban Babu, Mohan Babu aside. Though they were "ever-green" for almost all their career, its better left not discussed.
When we come to the next generation, the actors like Chiranjeevi, Nagarjuna, Venkatesh, Balakrishna, Kamal Hasan, Rajinikanth and many more, they started their career in the early 80's and almost all of them are lead actors (heros) even today in 2013. This is the same with Bollywood actors too. Shahrukh Khan, Salman Khan, Aamir Khan, and the likes have been acting in lead roles from 80s till date.
This factor does not (in bold letters) apply to actresses. The actresses have quite a short life span than that of the lead actors. They have to soon move on to acting in supporting and character roles once they start ageing. They even play mothers role to the same actor with whom they had acted against.
Some times the Heros remain Heros even when their sons start their acting careers as Heros. To explain this better, Sridevi, the actress has acted with actors like NTR, ANR and also with Balakrishna, NTR's actor son, and Nagarjuna, ANR's actor son.
Here are some of the pictures of the Heros when they started their career as young actors and then, when they got established as Heros, stayed as Heros for a "LONG" time.