There is an earlier mention of St David in a tenth century manuscript called "Annales Cambriae", it mentions the date of his death as being 601 AD. It is not possible to give any certaintly regarding dates, in fact I read somewhere that St David Lived to be over 100 years old!
His date of birth and death seem to verge on speculation, but I would think that sometime during the 6th century is vague enough to be correct! Born at Menevia (St David's) in Pembrokeshire, he was the son of King Sant of South Wales, his mother was St Non (Nonna), legend has it that Non was a nun and that she was defiled by King Sant, hence the birth of David!
Another legend tells that St David's birth was foretold some thirty years beforehand, by an angel who appeared to St Patrick. There is also a story about St Davids baptism at Porth Clais, where a blind man was said to have been cured by the baptismal water.
David founded or restored some twelve monasteries; one of those that he founded was at the site of the current Cathedral of St David's, Pembrokeshire. Other notable monasteries are those at Glastonbury, Bath, and Leominster. He travelled throughout Britain as a Missionary, and it is known that he also went to Jerusalem.