We camped with a group where most of the members were 75 and older. Several were past 80 and traveled in 35 ft MH or 35 ft 5th wheels. My Dad used to drive his 35 ft MH from California to Indiana and back every year when he was 80 through 83. He would tow a 16ft cargo trailer behind his MH.
We did ask my Dad to stop driving around 85 due to dementia. The Colorado Highway Patrol called me at 1:30 in the morning they had stopped Dad in his Jeep Liberty going the wrong way on 1-70 near Vail. I went and picked him up and he never drove after that.
One of the signs we missed regarding his ability to drive were new dents and scratches in his Jeep and MH and cargo trailer. Each time we would visit him I noticed new scratches or dents...he would claim they happened when he was re-positioning a vehicle or clearing brush. I now know it was due to his dementia.