Hi Maureen
You will spend three nights in Cuzco before going to Machu Picchu, which will give you ample time to acclimatise. I did something similar when I went and had no problems. Bear in mind too that altitude sickness doesn't affect everyone and isn't related to age or fitness - some people get it and some don't, but acclimatising is always a good idea.
You won't have to do any climbing that you can't manage - we will take you to a central point and then how much you explore is up to you. You will still be able to enjoy some incredible views without walking very far.
You are in for a treat!
Kind regards
Olly, your editor