The spotter question should not have anything to do with age, rather it should have to do with the population at the flight line. With two guys at the field, you really don't need a spotter. With ten, you probably do.

Large clubs should institute rules that requre every member to act as a spotter if there are more than 4 pilot stations occupied. The logical practice would be that the pilots in the bull pen waiting for a flying slot should be required to act as spotters while waiting their turn.