What age group is contracting the highest percentage of STI's?

Answer 1

Compared to older adults, sexually active adolescents (10- to 19-year-olds) and young adults (20- to 24-year-olds) are at higher risk for acquiring STDs for a combination of behavioral, biological, and cultural reasons. The higher prevalence of STDs among adolescents also reflects multiple barriers to accessing quality STD prevention services, including lack of insurance or other ability to pay, lack of transportation, discomfort with facilities and services designed for adults, and concerns about confidentiality. Recent estimates suggest that while representing 25% of the ever sexually active population, 15- to 24-year olds acquire nearly one-half of all new STDs.
http://www.cdc.gov/std/stats/adol.htm