Yes, it is generally considered rude to ask an elderly person why they are using a walker or any other assistive device. Similarly, it is also considered impolite to ask someone about their age, especially if the question seems to be related to their use of a walker.
Asking about personal medical conditions or physical limitations can be intrusive and may make the individual feel uncomfortable or embarrassed. It's essential to treat elderly individuals with the same respect and consideration as you would with anyone else. If you are genuinely interested in getting to know them better, focus on engaging in a friendly conversation about shared interests, experiences, or other topics that do not revolve around their age or medical conditions.