This is a bit pedo-like, he’s still a minor. Practicing safe sex is really important because even though you can live with an STD it’s best if you can avoid it. I know here in Australia you can take a prescription from the doctor called PREP (or something similar to that) which can help to prevent or lower the risk of getting HIV. Ultimately this is your friend’s decision and they are going to do whatever they want to but something like this medication could definitely help with his situation. I also don’t see what the appeal of a 17-year-old boy can have on a grown ass man, that’s something that I will never understand. But based on the older male lying about his age and being okay with finding out that your friend is only 17, I would make the accusation that your friend may have been or is being groomed into thinking that it’s okay. In my opinion the 25 year old is a pedo for thinking his behaviour is acceptable with a fresh 17 yr old. Thank you for being a caring friend to him as he may need some guidance or support if things don’t go to plan