The Tories rightward swing has made them un-electable in the eyes of most people in the U.K, and their voters are getting older every year (the average age of a Tory member is over 65... and it's almost that grim with their voters. Not as extreme a pattern as the CDU in Germany though...).
I don't know who told you the myth that the CDU is dying out (I suspect Lewis Trondheim ), but I can assure you it is not true.
You suspect correctly...the CDU is not dieing out, o/c - it's still much stronger than the Tories, across the board. But it's heavily skewed towards the generation now 60-80, and actually has been throughout BRD history (in the fifties, the CDU was the young voter's party). The CDU's youth problem, thus is an "everyone but the aged" problem, and its distributed very unevenly across the nation. It's worst in the cities (which is of course precisely where the Green votes are). Here's the Frankfurt European Elections result by age group.
18-24 Greens 30.6 CDU 23.9 SPD 23.3
25-34 Greens 32.3 CDU 25.1 SPD 19.0
35-44 Greens 39.8 CDU 21.1 SPD 19.8
45-59 Greens 30.8 CDU 29.2 SPD 20.5
60+ CDU 54.1 SPD 23.8 Greens 7.2
Greens gained 16 points in the 45-59 age bracket by the way - the last batch of "pre-68ers" turned 60 between 99 and 04...