I wrote that before I saw his age. Still, if he's in good health, let him set the pace and go for it!
My observation of my old guy is, other than what I consider to be in poor health due to age and previous owners care, the warmer it is, the slower we end up going or the more likely I'll end up carrying him, which I will gladly do when he gives me the "look". 65 and up degrees expected temperature gets me into the mind set of starting earlier in the day when it's 50-55 degrees. On walks, mine does better on cool days.