It does vary from country to country (and of course we can also assume that the UK puts a lot of money and effort into Aids awareness than Thailand does) and also my data came from AVERT.org and was for the period of 2005 to 2014 rather than a single year.
In the United States (which I would like to believe is a "developed" nation but sometimes I wonder if it is not becoming an "undeveloping" nation) the 13 to 29 year old group saw an increase in Aids infection and accounted for 39% of all new Aids cases in the USA.
When you hear about a young man dying of sexually transmitted diseases in another country we always try to "understand" and or "explain" the loss by coming up with some sort of "explanation" when there really isn't one....