DH

const INIT_AGE = 2020;
const END_AGE = 2022;

const calculateSoldsAmountBetweenAgesByParam = ({
  initAge,
  endAge,
  data,
  attribute,
}) => {
  return data
    .filter(({ Date }) => {
      const [day, month, age] = Date.split('/');

      const isBetweenAgeRange =
        parseInt(age) >= initAge && parseInt(age) <= endAge;
      return isBetweenAgeRange;
    })
    .reduce((acc, current) => {
      return {
        ...acc,
        [current[attribute]]:
          acc[current[attribute]] !== undefined
            ? acc[current[attribute]] + 1
            : 1,
      };
    }, {});
};

const getBestSold = (records) => {
  let winner = null;
  let maxSold = 0;

  for (const [key, solds] of Object.entries(records)) {
    if (solds >= maxSold) {
      winner = { [key]: solds };
      maxSold = solds;
    }
  }
  return winner;
};

const getWorseSold = (records) => {
  let winner = null;
  let minSold = null;

  for (const [key, solds] of Object.entries(records)) {
    if (minSold === null) {
      winner = { [key]: solds };
    }
    if (solds <= minSold) {
      winner = { [key]: solds };
      minSold = solds;
    }
  }
  return winner;
};

const main = () => {
  const soldsAmountByZone = calculateSoldsAmountBetweenAgesByParam({
    initAge: INIT_AGE,
    endAge: END_AGE,
    attribute: 'Zone',
    data,
  });

  const soldsAmountByStore = calculateSoldsAmountBetweenAgesByParam({
    initAge: INIT_AGE,
    endAge: END_AGE,
    attribute: 'Store',
    data,
  });

  const soldsAmountBySalesManAt2021 = calculateSoldsAmountBetweenAgesByParam({
    initAge: 2021,
    endAge: 2021,
    attribute: 'Salesman name',
    data,
  });

  const soldAmount = Object.values(soldsAmountByZone).reduce(
    (acc, amount) => acc + amount,
    0
  );

  const soldsPercentageByZone = Object.keys(soldsAmountByZone).reduce(
    (res, zone) => ({
      ...res,
      [zone]: (soldsAmountByZone[zone] / soldAmount).toFixed(2),
    }),
    {}
  );

  const bestSalesMan2021 = getBestSold(soldsAmountBySalesManAt2021);
  const worseSalesMan2021 = getWorseSold(soldsAmountBySalesManAt2021);
  const storeThatShouldClose = getWorseSold(soldsAmountByStore);

  return {
    soldsPercentageByZone,
    soldsAmountByStore,
    bestSalesMan2021,
    worseSalesMan2021,
    storeThatShouldClose,
  };
};

console.log(main());