Bay Area seniors, mostly males, who want to feel 12 years old again are advised to try their hand at paintball. This splattering sport is made up of teams who “shoot” each other with washable paint cartridges. It instantly took the Geezer back to the neighborhood warfare of his Marin childhood. There is a battlefield at American Canyon north of Vallejo open every Saturday and Sunday. All day admission which includes mask, gun and 500 paint cartridges is $55. It is practically impossible to injure yourself.