If it is too difficult for him to walk up and down the stairs, it is permissible for him to pray home but this is something only Allah knows about. Therefore, he should be told that this is between Allah and him.

My father is about 62 years old. He’s still pretty strong but just needs a chair to perform Salaah. Does he too have to go to the mosque (which is 3 minutes away from our house)? He claims that walking up the stairs of the building of the house is hard