When do wet dreams completely stop?

Wet dreams completely stop after the Yogi masters all the 6 stages of 'Sabija Samadhi' (also called Savikalpa Samadhi) through meditation on the Supreme and starts becoming an Urdhvareta. By the time 'Nirvikalpa Samadhi' (which follows eventually after mastering Savikalpa Samadhi) is fully attained, the Yogi will have become a complete Urdhvareta and will have no more wet dreams. However, care will have to be taken to ensure that wrong thoughts, deeds are not indulged in at any point of time to maintain this state free from wet dreams.

As one gets established in Sabija Samadhi, it leads to deep, uninterrupted, dreamless and blissful Nidra (sleep) at night. The Yogi does not require too much night sleep from then on and yet he is full of energy through the day. The body is fresh and the mind awake by 3.30 A.M or so, coaxing one to get out of bed and start Yogic practice. One feels a strong urge to meditate many hours in Samadhi from this stage onward. Blessed and fortunate is the Yogi who reaches this stage. In this stage, the mind is always in the thought of God with Bhakthi (devotion). I salute & bow to the Lotus feet of the great, Almighty Parabrahman with tears of Bhakthi and gratitude for the grace he has shown me. May my mind never be intent on anything but HIM. May all other honest Brahmachari-s also be blessed by his grace.

On the whole, for wet dreams to stop, the very strong and gross sexual Samskaras (impressions) and Vasanas (tendencies) in the Karana Sharira (causal body) have to be vacated through arduous practice of Yoga along with the grace of God. On reaching this stage, the milder impression's which are feeble cause mild desire when they occasionally surface (which the Yogi then displaces) but do not cause wet dreams. Entry into Sabija or Savikalpa Samadhi during meditation is the first physical sign of the beginning of this stage. Shri. Bhagavan Ramana Maharishi is referring to the state of 'Soma' or 'Amrit' (divine nectar) which is formed in the brain by the transmutation of Semen through the molasses-candy example you mention. This does not refer to gross semen. Semen formation stops upon reaching this stage further to establishment in the state of 'Soma' up in the brain which does not come down to form Rethas (semen), unless one loses Brahmacharya through voluntary, wrong action.

How soon one attains to this state varies from person to person depending on various factors such as one's intensity, regularity and honesty in unbroken practice. The strength of past karma and most importantly the grace of the Almighty is very crucial. Depending on all these, one reaches this state sooner or later. But it is to come, if the practice is correct, consistent and genuine. From my personal experience, if Brahmacharya is unbroken with regular Pranayama & meditation with devotion to the Supreme, any period upwards of 2 years or so of true, unbroken practice offers a very high possibility of reaching the initial stages of Savikalpa Samadhi. Again, generalizing time may not prove to be accurate as each person, his past karma and efforts vary in nature.

ॐ तत् सत्
(That Supreme being is the absolute truth)