A broken fingernail can seem to take forever to grow out if you're an adult. Children and young teens are the ones who get a lucky break -- their nails heal and grow back much faster. In fact, many parents can attest to cutting a squirming child's nails almost every other day. When it comes to nail growth, age and health play an important role.Nails are made of a protein called keratin, and their growth is affected by several different factors, including age and health. Children's nails grow quickly until puberty, when growth slows to 50 percent...