The simple answer is: no. Keeping long hair at any age, whether 4 or 41, does not affect the physical development of the body.
Since childhood we’ve heard this myth about long hair, if you keep long hair as a child that will affect your growth and specifically your height because that huge mass of hair on your head sucks up all the nutrients otherwise occupied by the body for its functions, but here’s the plot-hole to this story;
1. Your hair is literally dead follicles, everything except the roots is dead hair cells and it physically can’t suck up anything from your body even if it tried.
2. There’s set proportions for what goes where and how much, the body is a systematic machine, it doesn’t work on whim. So there’s regulated amounts of nutrition that’s divided to all body parts accordingly, and your brain, your head and your hair roots also only get as much as they need and are provided, not as much as they want.
This is one of those silly myths that we’ve all grown up hearing but have no scientific or even unscientific reasoning behind them.
So now you know! Long or short hair doesn’t affect your growth, the only thing that mostly affects your resistance to gravity is your genes and environment; this would mean that going bald would leave more food for your body to munch on?