Capshaw actually looks very good (not counting promo for next episode, did she filmed it right after giving birth? lol). And I think most people don't think that Meredith looks old, it's just they are acting like she is 25 y.o sex symbol who is getting all the hot guys, which is not really realistic, IMO.
Her makeup is also not very good. Makeup artists (or whatever they are called) are to blame. And she actually looks better in bright clothes, yet she is always wearing dark colors on show.