How can an 80-year-old man, who experiences frequent urination and remains lying on bed most of the time with a hanging bag, perform his ablution and offer his prayers?
It is very simple. Just he performs usual ablution as much as he can.
'Urine bag does not harm his ablution. If his urine drops continuously with out stop, then one Wudu is enough for every Salah. If there is a break with out urine dripping, he should perform Wudu during that purity break and perform his Obligatory Prayer.
Wassalam.