Welcome to HealingWell!
Is your brother on any medication? A lot of times "older" people begin having D when they start medication. Antibiotics are notorious for giving people D. Sometimes it can take months for people's GI tracts to recover.
Does your brother have acid reflux? That causes a lot of belching. *Acid reflux meds can cause D.* I'm not sure that belching is necessarily listed as an IBS symptom, BUT I do it a lot. There must be a connection there too.
You might suggest your brother try getting his gut back in balance with yogurt. Dannon Activia is great and even has a guarantee that things will begin to function normally in 2 weeks.
At your brother's age it is a fantastic idea to be scoped. Better to be safe than sorry.