The plugin takes some time to update the value. Try using the build in callback, ref: http://api.jqueryui.com/spinner/#event-spin
as a seperate event.
$("#age").on( "spin", function( event, ui ) {
console.log(ui.value)
});
or as a option on init
$("#age").spinner({
min: 1,
max: 99,
spin: function( event, ui ) {
console.log(ui.value)
}
});