I don't think 13 months is too old to introduce a dog to the nets, in fact there is a line of thought that says leave a dog to be a puppy until you start with the 'heavy' training.
What happens if you put a board across your doorway and call the dog - does it run straight into it? Obviously not, because somewhere in it's life it would have learnt to jump over it! The same will be said for the net, it will soon learn to avoid it. As for what it will do with the rabbits in the net then it's pretty much in line with what it does with them out of the net (on the lamp); does it hold them, retri