Every planet has a specific year of its activation or influence age. In the Bhriat Parashara Hora Shastra published from Mumbai this has been specifically mention. The age of 16, 22, 24, 26,28 , 32, 36 and 42 is the activation age of Jupiter, Sun, Moon, Venus, Mars, Mercury, Saturn and Rahu-Ketu. Depending upon the strongest or the weakest planet in your chart any of these above mention years could bring drastic changes in your life. As per this system the period of 16 to 22 years of age, 22 to 24, 26 to 28, 28 to 32, 32 to 36 and 42 to 48 years of age is ruled by Jupiter, Sun, Moon, Venus, Mars, Mercury, Saturn and Rahu-Ketu respectively.
Apart from this the Bhrigu Astrology/Bhrigu Sanhita system also consider 30, 36, 48, 60 and 72 years of age as the time that may bring very enigmatic changes in your life depending upon the running Vimshottari dasha. This principal is based on the transit of major planets Saturn, Jupiter, Rahu and Ketu over their natal positions. In Western astrology this is know as the planetary return system which is used in making forecast of important changes in life. Around the age of 30 years the Saturn completes its one cycle in transit and reaches at its natal position. At the age around 36 the Rahu-Ketu complete there two cycles of 18 years and the Jupiter complete its 3 cycles of 12 years each. So around the age of 36 Rahu and Jupiter will be reaching at their natal position in a horoscope. At the age of 48 the Jupiter completes its 4 cycle of transit ( 12 x 4 = 48) .