I am not sure what I think!
On the one hand - your GP knows nothing of your life and choices, so it's not really their business.
On the other hand - I guess they don't want to see you come back wanting IVF in a few years and feel that they didn't warn you? (or maybe it could be a concern about the drain on NHS funds!)
This actually happened to someone I know and she's only 30! She was 