Used to piss me off when I was a young'un, eating like a horse and putting no weight on whatsoever due to shitty high metabolism. So matter how much I ate I was still a 5"4 stick insect with a baby face (and an incredibly ugly one at that) who often could pass for 12 at age 17, and like you OP I got the whole "Eat up so you'll get big and strong!" bullshit. Even though I was eating MORE than any adult I knew, I even knew then there was no hope but no-one would shut up about it.
I can't win either, now that I'm 36 I would like to look a little bit younger, or at worst my age, but I done an r/rateme not long ago and passed for at least 55 on the best rating and almost EVERY comment mentioned how old and haggard I look. Plus I put weight on even THINKING about eating now, so am a 36 year old obese Manlet who looks close to 60.