
No, of course two maidens can certainly work, but you have a better chance of success if one at least is proven.
Also generally there is a lot to be said for using a young dog on an older bitch and older dog on young bitch regarding the resulting pups.
Obviously we can't wait too long before breeding from our bitches, (and also leaving males too late can mean a clueless stud),but many negative issues of health don't manifest until maturity/middle age.
So by having one of the pair older and proven healthy and hopefully already produced healthy typical offspring we are loading the dice in favour of a good outcome.
With two young maidens your still much more in the dark.
There's a young unproven male I'd love to use on my Inka, but I would not like to use him on her as she is awful in the tie, on two occasions she has done a 360' roll despite being held. Very keen to be mated but hates the tie.