I don't think the video is 18+ at all but I could say "viewer discretion advised" or something because the topics discussed are so heavy.
I have a disclaimer screen in the beginning that basically says "please don't be insulted by this video, my mental health impacts my ability to create a good video"
Maybe I could add a line at the top that says:
"Although intended for all ages, this video may cause stress, anxiety, or other lasting effects for anyone old enough to watch it."