If one is trying to offer and puts in whatever effort of will one can then one is not insincere. The effort may not always succeed for a number of reasons, most importantly because sexual impulses are rooted in the body and the subconscient nature and hence tend to persist and return tenaciously. Besides they are strongest during adolescence and adulthood and merely controlling their outer expression does not always help the mind to get rid of them. It is for this reason that Sri Aurobindo did not generally encourage very young people to take up this Yoga as it could destabilize the person due to violent surge of such impulses turning the mind and heart into a battlefield.
That is why the general advice to go through life, experience it, face its challenges and when one is truly ready and has the inner calling, say around 30 to 40 years of age, then take up the full practice of this yoga. Until then it is good to prepare oneself through study of Sri Aurobindo and the Mother’s Works, open to and have a growing inner contact with the Mother, come and breathe the Ashram atmosphere from time to time and practice the Yoga of the Gita, especially Nishkama Karma, offering of works to the Divine and Equanimity. All this while engaged in life until the moment comes when one is ready for the deeper plunge and grappling the forces of nature such as sex, ambition, fear and anger.
In any case sexual impulses resist a lot and do not generally concede to mental control alone. One has to practise inner detachment when they rise, quiet rejection which is not always easy, stay busy and do lot of physical exercises to sublimate these energies and divert them to helpful activities. Finally as a result of persistent aspiration and perseverance of effort, above all the intervention of the Grace it finally leaves though does not completely vanish. But it is weakened enough waiting for its transmutation into becoming not an instrument of degraded pleasure as it now is, but a means of union with the Divine and the bliss of that union. It is a long journey and one cannot hope to win the victory without much long labour.
Affectionately,
Alok Da