I know you live in India and it is hot there. It will be very hot on the VDLP at that time also. My friend walked it in 2018 and he started in mid September and he had temperatures of near or at 45C some days. He said he had to be off the Camino by 1:00PM at the latest. He left very, very early before the sun rose. I walked last year starting in Mid October. We had 30C+days out of Sevilla every day for at least 10 days. Very little shade. Bring one of those reflective UV umbrellas. I carried 3 liters of water (2 Frozen) with food every day. You need to plan ahead. Check to see if albergues are open or if you end up in a tiny village that there is a shop to buy food. Some nights I could not eat until 9:30 because that is when the bar would serve food. Met very few pilgrims during the day. Maybe 5 or 6 total. Usually there were a few in the albergues at night. There are long stages but if you plan you can do work arounds.
It is a very different camino to say the least. It took me a while after I got home to decide what I thought of my experience. I can't say I loved it or hated it at all. It was just really different and unique. I am glad I did it and actually would consider doing it again but starting in early March. Then, from what I have been told there are the rains to contend with. I am sure it can get messy then with all the little gulleys you walk through but for me it beats the heat any day!
Hope this didn't put you off but I didn't know how much you know about the VDLP. If you are into ancient history there is plenty to see. There are some very pretty towns to walk through. For me Merida and Salamanca were my favorites.
I think many will agree who have walked that this video although long will give you a good idea about the VDLP. He walked in summer. I doubt that the weather will be much different in Mid September. As you get much closer to Galicia I am sure temperatures will ease up alot.
Again these are just my observations of my personal journey. It could be very different for you and your wife. I am the same age as your wife and I just wanted to err on the side of caution as I do not know how much you know about the VDLP and how much hiking/camino experience you have. If you are not an experienced long hiker or have done a few caminos of course you can do it, but I would recommend doing a different camino. Also at least a working knowledge of Spanish is going to be important. I didn't meet more than a handful of people in restaurants or bars or albergues that spoke English. It is not a camino with good infrastructure like the Caminos Frances, Portugues or Norte. The local Spaniards are very nice but I never got the impression except for the albergue owners that they cater in any way to pilgrims as I do believe they saw the economic impact of their business from pilgrims was insignificant. As an example, and others may correct me, I could count on one hand the number of restaurants that had "pilgrim menus". But if you can do the VDLP you can do any of them. it is not the ultimate physical test but as caminos go I think this one, like many of the other long southern caminos are a big spiritual and mental test.
