yeah, that one looks rusty, but still rideable. These bikes were made to the same basic pattern for a long time, but my guess it's made somewhere in the late sixties or early seventies. The saddle is definitely a replacement (treat yourself to a fine sprung Brooks, or better yet, Lepper). The reflectors are probably later additions when the law on reflectors changed.

BTW, the odd top tube indicate that this was a boys' model: the idea was that by making the effective seat hight a little lower with that kink you could buy this bike for your teenage son before he had his growth spurt, so you don't have to buy him bigger bikes all the time. Thrifty Dutch solution that's just unthinkable in todays' disposable consumer culture.