Re: the “adult weight” of 87kg
At 1.78m and 68kg I think you're slimmer than average if you're male. You're the same height as me though ... anecdote:
My Doctor: "You are 15 Stone. Do you know your BMI?"
Me: "Of course, it's exactly twice my weight in Stone, 30"
Dr: "That's not how you calculate it"
Me: "It is if you are 5 foot 10"
Dr: *fiddles with calculator, then laughs* "do you spend a lot of time sitting around thinking about maths?"
Me: "Why do you think I'm so fat?"