Incumbent Manmohan Singh, 76, of the ruling Congress Party and 81-year-old L.K. Advani of the main opposition Bharatiya Janata Party (BJP) have both made efforts to appear the more spry and energetic on the campaign trail.
The Oxford-educated Singh underwent multiple heart bypass surgery in January, but made a speedy recovery and has not missed the chance to bring up the five years he has on his opponent.
Singh attributed Advani's accusation that he was India's "weakest" prime minister to his rival's "ripe old age" and suggested he change astrologers as he was clearly too old to change his views.
Advani, meanwhile, has been photographed lifting weights in front of supporters and has tried to reach out to younger voters with a blog.
Although both were born in present day Pakistan, they took markedly different routes to reach the corridors of power in New Delhi.
Unlike Advani, a career politician with activist roots, Singh is regarded as an accidental prime minister, a technoc