There is an entry in Hengwrt 33 V, NLW Cwrtmawr 453 (c.1615×1630) that states:
“The age of the Lord when Cadwaladr Vendigaid went to Rome: 653.”
There are two possible chronologies for Cadwaladr Fendigaid:
1. HRB XII 14 tells us his mother was a sister of Penda. This is confirmed by ByA 28a:
“Mam Gatwaladyr vendigait, merch Pyt, chwaer y Banna ap Pyt.”
where Panna ap Pyd is the Welsh for Penda son of Pybba. The Annales Cambriae tells us his father died at ‘bellum cantscaul’ c.632 to 634. Bartrum estimated her marriage to Cadwallon c. 632. Thus, AC dating Cadwaladr’s death in 682, during a plague, is plausible. That there was indeed a plague around this time is confirmed by entries in a number of Irish annals.
2. Bartrum argued that the plague in which Cadwaladr died actually occurred in 664. Reference to it is given by Bede:
“In the same year of our Lord 664, there happened an eclipse of the sun, on the third day of May, about the tenth hour of the day. In the same year, a sudden pestilence …”
The timing of the eclipse is accurate to within days, as the following reconstruction of the eclipse path shows:
The earlier date is supported by HB 64 which talks of his death during the reign of Oswy. HRB states Cadwaladr reigned for 12 years which would give a start to his reign close to the time of his Rome visit. Charles Oman argued that HRB dating his death in Rome to 689 is a conflation with the Wessex Ceadwalla.
The second of the two chronologies appears to carry more weight.
 Guy, B., 2016, 23.
 Bartrum, P.C., 1966, 91.
 Bartrum, P.C., 1993, 90.
 Sellar, A.M., 1907.
 Oman, C., 1921.