I am only 21 but have noticed two age spots so I suppose it can be any age. Ways to prevent them are to minimise your sun exposure and wear sun cream. Ways to get rid of them are Intense Pulse Light or other laser therapies or perhaps bleaching by a qualified practitioner.
that's how people get rid of them but it costs money.
i am only 10 and i already have spots, to avoid them don't have any thing to sugury or fizzy.i drink water and most have gone away.don't try to rub them off it makes it worse.