31.4.5 Comparatives with ambiguous meaning
Some comparative forms are used to express something that has a contrary meaning of what the word itself says.
alt = älter
old = older
Mann trank ein Bier.
An elderly man was drinking beer.
One could think that
means that the man is older than just old. This is not the case. It actually means that this person is not yet old, but older than young.
The other way around it does not work the same way.
still means younger than just simply young.