Question

About 45 percent of new HIV cases involve individuals between what ages?

Answer 1

I believe the answer is 15-24.
Younger generation tend to have more tendency to  be careless and conduct unsafe sexual interraction with one another.
Since it is very easy for HIV to be transmitted in sexual relationship without condom, the numbers would be particularly high from early teens to early adults

Answer 2

About 45 percent of new HIV cases that involve individuals between the ages of 15 and 24. Worldwide, about have of the new HIV infections reported are in people who are under the age of 25 years. In the United States alone, 76 percent of all AIDS cases are in men while just 24 percent are women. About half of the new HIV infections will occur in those who are considered adult age.