(...)
import { createSelector } from 'reselect';

const birthDateSelector = state => state.user.birthdate;
const countrySelector = state => state.user.location.country;

export const ageSelector = createSelector(
  birthDateSelector,
  dateString => moment().year() - moment(dateString).year(),
);

export const regionSelector = createSelector(
  countrySelector,
  country => regionHelper.getRegion(country),
);

export const isEligibleSelector = createSelector(
  ageSelector,
  regionSelector,
  (age, region) => (age > 18 && region === 'LA'),
);

(...)