Firstly, welcome to the forum, Big Dave!
There is no difference when it comes to age. Weihrauch are pretty good at keeping everything public. If they change a rifle it'll have a new model number.
If you buy either of these rifles you'll get an A1 piece of kit.
New rifles will have a 12 month warranty and you'll know they're legal and haven't been tampered with. Second hand rifles will be cheaper but condition will vary considerably, buyer definitely beware here, you could have a bargain or a piece of scrap...