Not bothered to read all the posts, but I'd like to tell the OP about my own 17 year old brother.
My brother turned 17 last month. He's 5ft10. Last year, when he was 16, he came to visit me and he was smaller than me. I'm 5ft1.
He's still very young looking - he pays child fare everywhere, which is kind of a good point. All his life, people have been making fun of him. When he started secondary school, older pupils would stand in front of him and tell him he was the right side for a blow job. He's always been tiny, and he's suffered a lot from it. IMO, he's just a cutie - blond hair, blue eyes, long eyelashes... but you know how other kids are. He's had to fight hard to be as popular as he seems to be. And I know his height still bothers him. He loved judo, and he couldn't go on because kids his age were to tall to fight him, and kids his heights were babies who didn't know anyhing about judo. He goes to the hospital twice a year - he also had a very serious problem when he was 8, that's the main reason why - and the doctors say there is nothing wrong with him. He'll grow up to be a wee bit smaller than 6ft, same as my dad - which is an ok height. Doctors say he's not lucky because he has a late puberty and he is also naturally small. They've offered him to take hormons, but he's been wise enough to turn them down - said he wanted to let nature takes it course.
But he's been growing up so fast in the past few months. He was about my size last summer, and now my mum is telling me he's taller than me. I can't wait to see him next week ! His voice has changed this year, his face is changing... well, to make it short, he's having his puberty at last.
I've been very concerned about him as well, please don't feel weird for writing this. And tell your brother he has nothing to worry about. I'm not saying he'll grow up to be a giant. But he'll be ok in the end. And I know how hard it must be for him. But he has to be patient... pretty hard to say when talking to a 16 year old who must hear nasty things all the time from his schoolmates. But he'll come out stronger. My brother had to deal with his problem, and he's developped a great sense of humour for people to overlook his size. People love him - he's really popular. He's started a band, he is the leader guitarist and singer. He's a great kid, and I just love him.
Please feel free to PM me if you've got any worries you'd like to share about your brother.
Take care xx