Devotional Service should start at early age, and not during old age.
The manifestation of unadulterated devotional service is exhibited when one’s mind is at once attracted to hearing the transcendental name and qualities of the Supreme Personality of Godhead, who is residing in everyone’s heart.
Srimad Bhagavatam 3.29.11-12,
If one wants to capture Him, one must undertake devotional service.
Srimad Bhagavatam 10.9.10,
One should not be impatient in discharging devotional service, but should take instruction from the spiritual master and execute them with patience depending on the mercy of Guru and Krishna. The successful execution of Krishna conscious activities requires both patience and confidence? The devotee thinks "Krishna will surely protect me and give me help for the successful execution of devotional service." This is called confidence. — The Nectar of instruction, Text 03.
The Hare Krishna mahamantra is also a prayer, for a prayer addresses the Supreme Personality of Godhead by His name and invokes good fortune by petitioning the Lord to allow one to engage in His devotional service.
Srimad Bhagavatam 4.24.69,
One who acts to serve Krishna with his body, mind, intelligence and words is a liberated soul, even within this material world.