You'll first want to try to figure out why his aim is off. Some possibilities:
He might just be experiencing a normal effect of aging; the urine doesn't always come out in a predictable way. It may spray, for example, or first may dribble and then come out fast.
He might have an underlying medical condition, such as a prostate problem or another cause of incontinence.
He might have poor eyesight.
When missing the commode becomes habitual, it's important to get a medical checkup to see if the cause can be determined. You should be frank: "You seem to be having trouble urinating into the toilet, and I just want to make sure there's no medical issue."
Matter-of-fact honesty is the best policy, even if you're embarrassed.
If you know that there's not a health issue or know that eyesight is the problem: Address the issue of cleanup in a supportive way: "Look, I've been noticing sometimes you miss the toilet. I'm going to leave a rag in a bucket here in the bathroom. If you can just check and wipe up any spills, I'd appreciate it, OK? I'll keep checking, too."
If he has dementia or another disorder that causes mental confusion: When the problem isn't just missing the commode but urinating in odd corners of the bathroom (or other places), the person might be trying to tell you something. In this case, don't say anything about the mess but pay special attention to see whether there's a pattern. Does he urinate outside the toilet only when a visitor comes to the house? Or when he's been left alone without company?
Someone with moderate to advanced dementia may use behaviors like this to express resentment, isolation, and other complicated feelings that they lack the capacity to share otherwise. The misplaced pee is a bid for your attention.
See if you can determine what the person needs. Some possibilities: more physical affection (being hugged while watching TV) or stimulation (getting out of the house more, perhaps by going out to eat or for a drive).