If Beowulf really existed he was born about 495 CE, which would make him a little younger than Arthur (if he existed). Arthur came to the fore at the Battle of Badon Hill, but that's put anyhere from 493 CE to about 517 CE. The Battle of Camlan, after which Arthur disappeared is put anwhere from 512 CE to 543 CE. According to Barber and Pykitt, Arthur gave up his kingdom after that battle and went to Britany, becoming St Armel/ Arthmael and dying at age 80 in 562 CE. However, much of their treatment is based on the discredited monastic records.

Known dates from Gregory of Tours puts Emyr Llydaw's (King Budic) death at about 556 CE, Riwal Mawr's (Hoel/Howel) at c 558 CE, and King Mark's (now married to a sister of Budic, not the first successor of Iseult) at Dec. 560, killed in a battle with the Franks.

These dates disprove a common old story that in it's most extend form has Gwyar, Arthur half-sister married to Budic and after Budic's death taking her son Hoel/Howel/ Riwal Mawr back to Cornwall to live with her father, Gorlois. Who Gwyar's husband really was I'm not sure, but her eldest son was Gwalchmei (Gawain). In the oldest Welsh tale, "Culhwch and Olwen" (where the sex of Gwyar isn't given) Gawain is Arthur's nephew through Gwyar and his cousin. That cousin part suggests that Gwyar was married to an uncle of Arthur on his father's side, no blood kin to Gwyar. Geoffrey of Monmouth, in Wales, probably used this to make Emrys Wledig (Ambrosius Aurelianus, not Emyr Llydaw) Arthur's uncle.

Some French scholar, on the basis of traditons of Brittany and some monastic records, thought that Riothamus, who fought from Brittany close to 460 CE, was the same person as Ambrosius Aurelianus, and this looks pretty attractive to me. Geoffrey Ashe took Riothamus to be Arthur himself, but one wonders if even Ashe really believed that. It does seem likely that Arthur's continental battles were likely based on the real ones of Riothamus.