When was Owain Gwynedd born?  Here’s the truth:  no idea.

Okay, that’s not entirely true.  Like Llywelyn ap Gruffydd, nobody seems to have recorded the date Owain Gwynedd was born, or even the year.  This is fine as far as it goes, because we can make some general estimates.  The problem arises when the birthdays for his many, many children haven’t been recorded either.  Nor his siblings.  Nor the dates of his marriages.

My go-to-guide, John Davies History of Wales doesn’t discuss birthdays or ages, probably because he knows it’s fraught with difficulties, but many web sources try.  For example, here’s one huge root of the problem, the Wikipedia entry, citing a book by John Edward Lloyd  A history of Wales from the earliest times to the Edwardian conquest (Longmans, Green & Co.) written in 1911.  This has Owain born c. 1100, and a long list of his offspring  (http://en.wikipedia.org/wiki/Owain_Gwynedd):

Although I have edited the entry on Wikipedia to reflect the uncertainty of the birthday, if we’d continued to follow the 1911 source, Iorwerth ab Owain Gwynedd, the eldest son of Owain’s first wife, Gwladys, would have been born in 1145, a year after Dafydd ab Owain Gwynedd, the eldest child of Owain’s second wife.  Such a date could be possible for Dafydd, since he is first mention in the annals of wales in 1157. At the latest, that means he was born in 1143/44, since Welsh boys become men at the age of fourteen.  Obviously, we now have a problem.

It gets worse.  The Castles of Wales site, normally very reliable, has Owain Gwynedd born as late as 1109.  While neither Rhun nor Hywel get birthdays, they were full grown men by 1143, when Hywel is tasked with rousting his uncle Cadwaladr out of Ceredigion. If that’s the case, you have to think he’s at least 20 at the time.  If this is true, however, for Hywel to be  20 in 1143, he would have to been fathered by Owain at the precocious age of 14, and his elder brother Rhun even earlier.  Not impossible, but…  http://www.castlewales.com/owain_g.html

Furthermore, Citing The Mammoth Book of British Kings and Queens (by Mike Ashley, Carroll & Graf Publishers, Inc. New York, 1998), elsewhere on the site, it makes the claim that Owain was born c. 1100 (so I give them a pass on that), but now Dafydd, the eldest son of his second wife Cristina, was born in c. 1135.

Deeper into a search, the EBK site reports that Owain’s father, Gruffydd, married Angharad in 1195 (when he was 40) and had three sons (Cadwallon, Owain, Cadwaladr) and some daughters, including the youngest, Gwenllian.  http://www.earlybritishkingdoms.com/bios/gruffcgd.html  Fine. But it is Gwenllian who elopes with the much, much older Gruffydd ap Rhys in 1113.  Whoa.  http://en.wikipedia.org/wiki/Gruffydd_ap_Rhys  Note that the particular entry on Gwenllian, which actually has citations, not all of which I have access to, has her born c 1197, which by necessity must push all these other dates back into the earlier 1190s to make any of this work.  Unfortunately, to push those dates earlier is problematic, because Gruffydd was imprisoned for between 12 and 16 years, starting in 1081, so the earliest date of his release is 1093. http://en.wikipedia.org/wiki/Gwenllian_ferch_Gruffydd