Findings from contemporary research on aging and intelligence suggests that adults who cognitively engage themselves more in challenging jobs, or with intellectual hobbies, fair better in terms of the maintenance of their intelligence throughout middle and late adulthood. this finding fits best with which theory of successful aging?

Activity theory

Explanation:

Activity theory is the theory explains that people are embedded with each other culturally, socially and environmentally. Many theorists provided the hierarchical structure of motivation for people's actions.

The activities are taken by the goal-oriented action that is taken consciously. The constituents are fixed but activities of human beings are not fixed. These are dynamic. This theory includes the mediation of the theory culturally and socially.  

Thus the findings of this theory are best suited to the theory of successful aging.