The old custom of sending "Valentines" on 14th February has nothing whatever to do with St. Valentine.
The only connection between the day and the Saint is that, by chance, the saint was clubbed to death in Rome on that day. Young people for generations before had followed the custom of selecting a lover, and exchanged gifts on 14th February, which from time immemorial had been regarded as the day on which birds began their mating. It is probable that the custom, too, had something to do with the Goddess Juno and her worship.