i would say that starting markmanship with a youth .22 is ok as long as he is fully capable of understanding the seriousness i have met 6-7-8 year olds who are very intelligent. bruce i love ya man but i gotta disagree i think it is different for all i know people who are 30 that dont need to see a gun let alone touch or shoot one. i might start with a bb/pellet gun plinking first i read an article about kids needing instant gratification and the ting of metal lets them know they did good with out you saying a word. At the same time as for marksmanship if he only knows one way then thats what he will use so find one set way and use it for a while DONT CHANGE HABITS AND TECHNIQUES he is six i teach soldiers to shoot 40 out of 40 who have never held a gun before because we teach them one way i would start him with a stable base and have him shoot off of that like a good shooting stick even if it is a pellet gun. remember hes six and comparitively week that .22 will feel like a 12 gauge to him.
go get em