I'm not too sure about graffiti but Lisbon seems to really encourage it. I love the idea of old folks getting involved!
"If you’ve ever thought you’re too old to try something new, take a look at this and think again. A non-profit organization in Lisbon, Portugal took “arts and crafts” to the next level and taught a group of elders how to graffiti their way around town! Graffiti, or street art, has typically been an art form for those of a younger generation… until now.
This is a wonderful example of how art, fun and a positive attitude can eliminate all generational boundaries. Just put a can of spray paint in someone’s hand and set them free and watch them become a kid at heart!"