Well done Louise, hope they come back to you soon!!
Carys, Dave was 4 months when I re-homed Storm (she's 2.5 yrs) so it can work..
It's a lot of hard work and a little nerve wracking at times and you have to be prepared to do a bit of separate walks and training but it is possible depending on characters of the dogs etc.. I'd agree with you wholeheartedly that Griff is a very calm, sweet natured little chap so they could compliment each other ad he might help with her confidence - it was because Dave is so laid back on walks that I even considered taking on an older re-home..
Suspect the issue here is more whether you feel ready or not to take on that responsibility/challenge yet. 2 dogs is very different to one and Griff won't get the levels of attention he's been used to and if her eyesight isn't good and he starts messing around with recall etc, you may have a spot of bother there. However, there is also the old jealousy factor and mine compete to be better behaved than each other at times too so there is a possibility that that would happen. As she's quite a bit older than him it might well work... although you obviously have Griff's teenage years coming up soon too and this is where I'm expecting a bit more trouble with my two!
Hannah x