import moment from 'moment'

const today = moment()
//=> moment("2019-08-23T23:30:02.478")

const birthday = moment('1985/11/30', 'YYYY/MM/DD')
//=> moment("1985-11-30T00:00:00.000")

today.diff(birthday, 'years')
//=> 33

today.diff(birthday, 'years', true)
//=> 33.73327554263117

Math.floor(today.diff(birthday, 'years', true) * 10) / 10
//=> 33.7

moment.duration(today.diff(birthday)).as('months')
//=> 404.77148837872556

moment.duration(today.diff(birthday)).as('months') % 12
//=> 8.771488378725564

Math.floor(moment.duration(today.diff(birthday)).as('months') % 12)
//=> 8

(() => {
  const y = today.diff(birthday, 'years')
  const m = Math.floor(moment.duration(today.diff(birthday)).as('months') % 12)
  return `${y}歳 ${m}ヶ月`
})()
//=> 33歳 8ヶ月