Devotional Service should start at early age, and not during old age.
In the preliminary phase of spiritual life there are diffrent kinds of austerities, penances and similar processes for attaning self-realization. However, even if an executor of these processes is without any material desire, he still cannot achieve devotional service and aspiring by oneself alone to achieve devotional service is also not very hopeful, because Krishna does not agree to award devotional service to merely anyone. Krishna can easily offer a person material happiness or even liberation, but he does not agree very easily to award a person engagement in His devotional service. Devotional service can in fact be attained only through the mercy of a pure devotee.
Devotional service is not a job, it is a privilege.
Although karma, jnana and yoga are discussed in Bhagavad-gita, the only purpose is to inform us of Krishna’s greatness and engage us in His devotional service.
Lecture on "Understanding Krishna through Bhagavad Gita" – Salem – 8th Nov'06
Loving devotional service to the Lord begins with hearing about the Lord.
Srimad Bhagavatam 1.7.7,