Most of the cracks regarding Donnhoff's "inability" to age (at least at my end) are mainly tongue in cheek. It's been a bit of a talking point among some people as to whether Donnhoff's wines actually improve with time, just hold without really developing or fall apart, and there've been some pretty vocal critics who argue that Donnhoff's wines should be opened young and that older vintages (from earlier in the 2000s and older) are on the downslope.
As far as the debate goes - the issue is that a lot of older Donnhoff bottlings have come either from gray market sources and/or pretty iffy provenance. I attended a dinner in NY a couple of years ago where we did a
vertical of Niederhauser Hermannshohle (that was almost entirely Donnhoff), and the group sourced a bunch of older vintages from Dee Vine in California.
All the old wines (from '98 through '83) showed horribly that evening and only the younger wines (02 onwards) provided real enjoyment that evening. I've had a few other older bottles at some of these dinners (almost all sourced from DVW or places like Winebid or Flickinger) and very few were really impressive - some just came across awkward and tired, others showed signs I took to be heat damage.
OTOH - older Donnhoff from better sources (David Bueker's been buying and cellaring them for quite a while, and he's been generous enough to open a number with me) have generally been fantastic. Have had some stunning older bottles of Spatlese and Auslese (as well as a '99 Dellchen Kabinett a couple of years ago) that were simply exceptional wines, and given the balance and structure the young Donnhoffs have, I have no concerns about them not aging.