I was just in Italy with my 73 year old mother who has a replacement ankle. We did Florence and Tuscany.
Agree with the earlier poster who said Florence was manageable but there isa a fair amount of standing and walking since the primary sites are churches and museums.
Some of the hill towns are also okay -- San Gimigniano was workable and Siena might be okay if you can get to central parking. We also went down to Assisi which was a bit more ambitious (unless you just want to go to the main St. Francis church).