My dog keeps peeing in the house.?

we have a dog that's about 13 yrs old now. he keeps peeing everywhere in the house and i have to keep cleaning over and over again which is annoying. he's our first dog, we trained him, we take him outside and he was very spoiled. i can't seem to figure out why he is peeing all over the house when he just came from outside. :/ if anybody would kindly tell me what's the problem of why our dog is doing this or what should i do i'd truly appreciate it. thanks! *we also have 2 other dogs (younger) that don't pee in the house.