Reasonable suspicion does not apply if a person simply refuses to answer questions or is of a certain ethnicity or race. If a person is suspected of committing a violent crime, such as robbery or murder, the police officer may frisk the suspect's clothing to check for weapons.
Middle age technically refers to reaching an age where you have lived half the average life expectancy for your gender. The average midpoint of life is now about 40 for women and 38 for men (men tend to die 6 to 8 years before women). In comparison, 100 years ago women arrived at middle age by 22, mainly because so many died in childbirth.
60 to 70 is on the young side of being elderly. 70 to 80 is the middle of being elderly. 80 to 90 is definitely elderly. That is if you judge by age. Look in the obituaries and you will see many never reach the age of 60. I know people in their 80's that are in better health than those in their 60's.