Rennin and lactase, the enzymes required to digest milk, disappear in the human body by the age of

Rennin (chymosin) and lactase are highest in infancy to enable milk digestion and, in standard school-exam treatments, are said to disappear by about two years of age; thus many MCQ answer keys list “two years” as the correct choice . More detailed clinical sources show lactase activity peaks postnatally and then declines thereafter, with timing and degree of decline varying between populations; this supports an early‑childhood reduction in milk‑digesting enzymes though exact timing is variable and often gradual rather than an abrupt loss [1]. Given the options, “two years” (option 1) is the best single-choice answer for typical exam keys.

Sources

1. [1] https://www.ncbi.nlm.nih.gov/books/NBK532285/