Hi and welcome to the site!
My apologies for missing your thread before.
Yes, it is uncommon for people in their golden years to get IBS, but it's not unheard of. Is your only symptom stomach pain?
If the Mebeverine is not working for you, you should be able to request another from your doc. There are several antispasmodics out there to choose from. You just need to find one that works for you. In the meantime, you could try a heating bad to your abdomen. Drinking a hot cup of tea with a heating pad works wonders for me. Lately my IBS has been acting up big time, so I've been living with tea in 1 hand and the heating pad remote in the other. Boo!
Good luck! Please keep us posted on your progress.
Co-Moderator IBS Forum