i would like to get the number (here 2) about how many peoples age are under 20.

people = [
{id: "1", name: "abc", gender: "m", age:"15" },
{id: "2", name: "a", gender: "m", age:"25" },
{id: "3", name: "efg", gender: "f", age:"5" },
{id: "4", name: "hjk", gender: "m", age:"35" },
{id: "5", name: "ikly", gender: "m", age:"41" },
{id: "6", name: "ert", gender: "f", age:" 30" },
{id: "7", name: "qwe", gender: "f", age:" 31" },
{id: "8", name: "bdd", gender: "m", age:" 78" },

]

Thanks for help.