He said he was officially diagnosed a little over three months ago, that's one month before he met her, and that means he was having syptoms and seeing a doctor well before an official diagnosis.
A lot of people that age develop mental health issues, it is not uncommon, that is why most suicides happen in the late teens thru mid 20's. It's a brain chemistry issue. On top of which he's talked about dealing with mental health issues before (look at the vid that was posted) during his late teens, he just wasn't officially diagnosed.
Trans persons tend to deal with a lot of mental health issues, for a multitude of reasons. I seriously doubt Icky has been "putting thoughts into his head" to cause him to have a major depression diagnosis. She has her own issues as a trans woman, and sees a therapist herself.
