Hi Duayne,
Sorry for late reply - unfortunately I don't often visit the forum now, since we actually live in Povoa de Varzim!
We're both well over 60 (so young!) and have done the Vila do Conde to Rates in a day, no problem. A lot depends on the temperatures during the day, as you can imagine. There are quite a few stretches along secondary roads in the VdeC > Rates route. One just has to be a bit careful as in general (but not always of course) Portuguese drivers use excessive speed inappropriately. The usual culprits (again not always) are younger males and van drivers, as you can imagine!
However, a further 10 minutes on the metro and you're in Povoa de Varzim, and the start of the paved ecovia / cycleway is within 100 metres or so of the metro station. The distance from the Povoa metro right to the middle of Rates (the albergue) is 14km and following the ecovia couldn't be easier! You'd be in the open countryside after about 2 or 3km from the start. To me it's the obvious choice and it's very pleasant, quiet countryside.
Send me a private message if you'd like to exchange emails, or cell numbers. If we're not otherwise occupied at the time we could walk part of the route to Rates with you, although we normally cycle to Fontainhas, a furhter 3km, for their delicious coffee and pastries! (pasteis de nata!)
Wishing you a great Caminho!