I have an inguinal hernia. At what point should I stop living with it and insist it is fixed? It is gradually getting worse.

Now. When a hernia starts causing symptoms like pain and / or discomfort, it should be fixed.
Get it fixed. Inguinal hernias will tend to get bigger and more problematic. As we get older the risk of surgery and general anesthesia also increases. I would address the hernia sooner than later.
Pain/Enlarging. While not all hernias require repair, we generally recommend elective repair if one is healthy enough to tolerate surgery and the hernia is interfering with one's quality of life or has reached a size where intestine has the potential to get stuck (incarcerated) within the hernia sac. Since yours is gradually getting worse, it sounds like its time to have surgery. Good luck!