Is a tourist allowed to walk on the Great Wall a good length of it? I am an old person.

Hey, of course you can walk on the sections of the wall. However, some areas may not be open to the public. Therefore, you can not have a walk on these parts. Sections like Badaling, Mutianyu, Jinshanling and Simatai are equipped with cable cars. If you can't walk too much, you can choose to use the cable car to reach and get off the wall.