Rennin and lactase are enzymes necessary for digesting milk. These enzymes are more commonly present in individuals during the early stage of their lives when milk is a primary source of nutrition.

Option 1: Two is incorrect because the body doesn`t lack these enzymes as soon as two years of age. Most toddlers at this age are still able to digest milk very well.

Option 2: Three is considered the correct answer to this question. Many people tend to start losing the ability to produce these enzymes around this age. The age varies, however, and some people may continue to produce lactase beyond this age.

Option 3: Five is not correct as the majority of individuals have already started to lose the enzymes by this age.

Option 4: Eight is wrong because it`s much older than when most people usually stop producing these enzymes.

It`s important to remember that the timing varies among individuals. Some people never stop manufacturing lactase and can digest milk without problems their whole life. This condition is known as lactose tolerance.