const input = [{name: "name4", age: 12}, {name: "name3", age: 15}, {name: "name1", age: 10}, {name: "name5", age: 10}, {name: "name6", age: 15}, {name: "name7", age: 15}]

output: [{age: 10, count: 2}, { age: 15, count: 3}, { age: 12, count: 1}]