It seems to me that in Canada at least, "old" when referring to people has become a bad word. "Elderly" or "quite elderly" is used often.
I am in the bed and breakfast business. Some time ago we had guests from China. A three generation family. The oldest member was the 90 year old grandmother. Her son introduced her to me and mentioned that she was "very old". I chided him somewhat by saying "That's impolite, telling a lady's age!"
He told me that no, it is very important in China to be proud of your age, and that the old people are revered. I wish it would be like that here. I know that there are Chinese members here on this site, am I right in the assumption of age being revered?
So what I comprehend from this all is that elderly is somehow more formal and polite and usually is used for people? Can we use to for other things?
Yes, elderly is used for people. Old can be used for the animate and inanimate.
Elderly is considered a more polite term than old.
People also use 'older' as a softened form of 'old'.
An elder is a respected member of the oldest living generation of a group, tribe, congregation or other body of people.
Posted on public transportation: 'Please reserve these seats for the elderly and disabled.'
'Is Mr. Roberts here?' 'Yes, he's the elderly gentleman by the door.'
'I need a new backpack. This old one is worn out.'
'When my grandmother was a very old woman, she lived with us.'
'The older members of the staff can remember when the company was founded.
The council of elders gathered to discuss issues that will affect the future of the church.
The term 'senior citizens' or just 'seniors' is sometimes used (AmE) to refer to people over 65 or 70 years of age. This usage is impersonal and often used in government publications.