require 'date'
european_date = '%d/%m/%y'
puts Date.strptime('2/9/07', european_date).to_s # => "2007-09-02"
puts Date.strptime('02/09/68', european_date).to_s # => "2068-09-02"
puts Date.strptime('2/9/69', european_date).to_s # => "1969-09-02"