Aren't we all looking for some romance in our lives, regardless what age we are ... ? Surprise that friend who would not expect a Valentine's card ... :-)
Originally Valentine's Day was for forbidden love, when you would be in love with someone who would be married (for instance) and you'd send them an anonymous Valentine's card ...
It's also nice to send a card to someone you fancy but do not know if they return your feelings ... best of luck! :-)