The weather in Le Puy en Velay is going to be a little cold for me during the middle of April, with temperatures possibly as low as -3 Deg C until the end of April. Temperatures start to pick up in May, but starting then would mean I would still be walking in the middle of July and would hit the crowds that start in Sarria, something I want to avoid. The April weather in St Jean Pied de Port on the other hand is a little more conducive for the kind of walking I like to do, with low temperatures of around 8 to 11 Deg C and highs of between 16 and 17 Deg C. This weather pattern for St Jean seems to continue until May when temperatures start to rise.
Given this weather pattern, I think a start in St Jean would be better for me and I can always come back another time to walk from Le Puy to St Jean when the weather is more suitable for me. Also, if I start from St Jean, not only will it be cheaper because of the shorter distance, my pack will be lighter as I will need to carry fewer items of clothing to offset the cold weather.
Now, since I want to finish at the end of June at the latest and working backwards 40 days from there, I would need to start walking around the 21st May. However, given the weather pattern in St Jean during April, it also means I can decide to start walking anywhere between the middle of April and the third week in May.
I’ve heard that an area of the Camino known as the Meseta, that can be quite hot, dry and arid during certain parts of the year, so I need to figure out when that is and if it will influence my start date, so I’ll shoot off now to do yet more research.