"If I had any advice for my 16-year-old self"
Don't let ANYONE take nude photos/videos of you unless you are OK with them being made public.
No matter how much he says he "loves" you.
"... my 16-year-old self"
OUCH!
In the USA, laws governing child pornography cover children, (yes I did mean "children" in the sense of those laws), photographed undressed, or worse, and those photos/videos are legally considered child pornography. Possession of child pornography is a serious crime under those laws, as written, and even a selfie taken by a minor, even one day under age 18, is a crime for that same person to possess, and a separate crime to have produced child pornography.
(NOTE: This is not an entirely new thing with laws. Johnny Carson was interviewing a young actress, (12 or 13 YEARS OLD) Brooke Shields, and eventually asked her what she thought of the movie that just came out. She replied that she had not seen the movie, even though she was in it, because it was rated "R", and she was too young to get in the movie theater! It was a major motion picture, and "some things" were not then covered by the laws that are covered now.)
There are scandals in high schools where multiple boys and girls have shared their own selfies, and the police are struggling with who to charge, and with how many crimes, because most of the students have some, or all, of those photos in their phones. Having shared those photos is also legally considered distribution of child pornography, and worse than possession. BTW, the latest published report on one of those scandals is that the police will be filing criminal charges on the students who possessed multiple other students' photos, and they are trying to decide what to do about the phones that only hold such a selfie of that student... It gets more complicated if any other student also has that photo, since that indicates it was "distributed" somehow. Then there is still the question of producing child pornography.
Soooo,
it is a REALLY bad idea to even take a nude photo (selfie) or video of yourself at age 16.
Until the law(s) get updated, that is a huge risk the kids may not know about.
Plus, the risk is not only to that kid...
And if a kid forgets their backpack (containing their phone), asks a parent to bring it to them, and that parent is stopped by the police (for whatever reason), and such a photo is found in their unknowing possession, the law is clear, and they can be charged, convicted, and jailed for possession of child pornography.
(If you don't believe that, find the movie SNAP DECISION, and watch that.)