According to the fivenineclimber database http://fivenineclimber.com/bikes/gazelle/misc/serial_numbers.htm #2227561 falls somewhere around 1968 - Seems a bit odd given the rear brake cable guide braze-on's on the top tube - didn't think they came into play till the late 70's (builders previously believed that brazing would weaken the tubes, so everything on race bikes was held in place with little crome clips)
Hope this helps - the fivenineclimber page is pretty handy for all things Gazelle - here's a late 70's frame with top tube cables http://fivenineclimber.com/bikes/gazelle/ramos_red.htm
According to the fivenineclimber database http://fivenineclimber.com/bikes/gazelle/misc/serial_numbers.htm #2227561 falls somewhere around 1968 - Seems a bit odd given the rear brake cable guide braze-on's on the top tube - didn't think they came into play till the late 70's (builders previously believed that brazing would weaken the tubes, so everything on race bikes was held in place with little crome clips)
Hope this helps - the fivenineclimber page is pretty handy for all things Gazelle - here's a late 70's frame with top tube cables http://fivenineclimber.com/bikes/gazelle/ramos_red.htm