you have to both be over 21 if your applying for a spouse visa, fiancée visa, or unmarried, same sex and civil partners visa's.
but if your a EEA national exercising your Treaty rights in the UK, then having to be over 21 doesn't apply to you if your applying for a family permit for your wife

and also it doesn't apply to dependent visa's (e. g.student visa,tier 2)
