Should I be worried about my father (86) at home alone?

Pam is so right on this! Just being 86 and a complainer doesn't disqualify one from living alone. Keep an eye out for signs that he is declining.

Sounds to me like he's doing pretty well for his age. As long as you visit weekly he is good. While you are there, look for scorch marks on the pans, rotten food in the fridge and sneak a peak at the mail to be sure bills are paid. If he has taken the batteries out of the smoke detectors, that is an indication he's burning things. Little signs are important, so be aware. Is his car covered in scratches or unexplained dents? Look.