Which Indian state is beginning to acquire an age structure like that of the developed countries?

Kerala

The correct answer is Option 1: Kerala

Kerala  is beginning to acquire an age structure similar to that found in developed countries. It has experienced lower birth rates, lower death rates, higher life expectancy, and a growing proportion of elderly people. As a result, Kerala is witnessing the process of population ageing earlier than most other Indian states.

NCERT: "As with fertility rates, there are wide regional variations in the age structure as well. While a state like Kerala is beginning to acquire an age structure like that of the developed countries, Uttar Pradesh presents a very different picture with high proportions in the younger age groups and relatively low proportions among the aged. India as a whole is somewhere in the middle, because it includes states like Uttar Pradesh as well as states that are more like Kerala."