We reach our physical peak (fastest reaction time, most acute sensory awareness, and highest cardiac output) during which year in our lives

20 - 29

Explanation:

Our physical capabilities tend to develop over the years and started to grow rapidly after we hit puberty. But the rate of our physical growth tend to vary between individuals.

It all depended on our nutrition, exercise and genetics. (mostly genetics. Nutrition and exercise only enhance the possibilities that provided by the genetics).

This number is supported when we look at athlete's performance. Most of them have their best years between that age group and started to deteriorating after they pass 30