This is something that comes up a lot on here so I thought it worth making this recommendation.
I have bad dark under eye shadows (genetic ones) and the full coverage concealers like Benefit Boingg that were perfect when I was a bit younger now look cakey and settle in the fine lines under my eyes.
Boots No7 Hydro-luminous Under Eye Concealer (in a blue tube) is the best compromise I've found. Although it doesn't give the same coverage, it doesn't cake or settle in lines and it goes on smoothly like an eye moisturiser. It covers a bit (not all) of the shadow but lightens and brightens too. Also not that expensive. Not as good coverage as the Collection one (also good and cheap) but a much dewier look which I think is flattering on older skin.
You can probably tell I have tried them all :-) and I think this is a good one for older skin so I wanted to come on and recommend it.