I belief there are a few problems that Chelsea are having this season... One is the training style is not good enough and Scolari seem to favour a more relax kind of way... Lampard and Terry have openly come out to questioned his relax style in training and feel that they are not doing enough. I also think we can see that the current Chelsea players are not as fit as say just 9 months ago... So to say their age is the main factor, I don't think so cos all their defenders are in their prime... Bosingwa 26, Terry 28, Carvalho 30 , A Cole 28... Even Alex is only 26... Cech also 20+ only.
Another thing could be Scolari inexperience in the Premiership cos Chelsea started the season rather well without too much problems... They were even leading the table with Pool. The Dec / Jan period was probably the difficult part Scolari isn't aware of... There are lots of matches to be played this period and playing his first team for the Carling and FA cup is rather silly... Top players need their rest or they won't be able to perform at the highest level week in, week out...
I honestly belief the problem is Scolari and not the players... Scolari don't know how to handle them, just like Drogba who also played well for Grant but he don't seem to be interested to play for Scolari... Maybe its because Scolari don't show enough concern for him...
Change Scolari and Chelsea will be back again...