I've been to India a good few times as OH is originally from there. We got married in India and my parents and uncle went there for the wedding. They were in late 60s and did some travelling around to tourist places after the wedding. That was in early 1980s when facilities weren't as good as now, and they enjoyed it.
Some aspects of India are a culture shock, but most tourists stay in good hotels and have a car with driver. In earlier years, our trips were mostly visiting relatives, but pre-Covid we did a few touring holidays, and had no problems, despite being in late 60s. We did it independently, booking flights, trains, hotels etc. as I enjoy all the planning! There are lots of package trips available too.
If your children have been they may be able to advise you on where to go. Personally, I prefer the South- Kerala and areas around. Trains are a good experience but flying is easier when older.