I am 19 yr old. last september or october, i hadn't lot of hain my arms and chest, but now in april i have..and on arms, hairs are around 1 inch! why?

Usually familial: Hair growth patterns run in the family. A male with a particular pattern can look to see if his father, brothers, male cousins, or uncles have a similar hair pattern. If he feels he is very unusual, he can see his primary care doctor or a dermatologist for an opinion.

Lucky you!: Many men who are going to be hairy don't get it until they're 20 or so. I hope you're pleased with whatever Mother Nature gave you. If not ... shave for now, and let your future partner decide whether to "manscape" you, send you for electrolysis / laser, or leave it as it is. I hope also that you'll cherish this time, and the increased joys and responsibilities that come with being a man.