Shanghai Airlines has relatively old 757's and 767's though these are well maintained and in most cases leased from large western financing companies.

Their 737's, on the other hand, are next generation models and actually quite new.

China Eastern has some rather old MD90's and A300's in circulation, but it's A320 family and A330/340 aircraft are pretty modern.

I would add that both carriers have aircraft that are towards the younger end of the age range of planes flown by the likes of Delta and American Airlines. I have no hesitation flying either airline.