Life line timing
Drop an imaginary line from the middle of the index finger to the life line: this is roughly age 10 to 20. A line from between the index and middle fingers marks roughly age 30 to 35. A line from the middle of the middle finger marks roughly age 40 to 50.
Fate line timing
The fate line is read from the wrist upwards. It traditionally meets the head line at about age 35 and the heart line at about age 50.
Marriage line timing
The space between the heart line and the base of the little finger represents roughly ages 15 to 75, with the middle around the late twenties to thirties.
Keep it approximate
Hands differ in size and proportion, so timing is always approximate. Astrology's dasha system can give more precise timing.