On trains, The young usually stand up and let elderly people have their spot. Say " you are standing but you see a free ( empty also works?) Spot and an old man gets on, would saying , "excuse me , there is an empty spot where you can sit" make sense? Yes, that makes sense. You could also say 'seat': "There is a free seat there".

you are standing but you see a free/ empty Spot and an old man gets on, would YOU SAY , "excuse me , there is an empty spot where you can sit