If what you mean by the "percent of people 50 years old belong to group A" is the percentage of 50-year old people with respect to the total number of people belonging to group A, then the answer is
32/(19+32) * 100 = 63%
But, if what you mean is the percentage of 50-year old people in group A with respect to the total number of 50-year old people, then the answer will be
32/(32+24) * 100 = 57%
