You can use _.mapValues(users, function(o) { return o.age; });
in Lodash and _.mapObject({ one: 1, two: 2, three: 3 }, function (v) { return v * 3; });
in Underscore.
Check out the cross-documentation here: http://jonathanpchen.com/underdash-api/#mapvalues-object-iteratee-identity