A friend commented that new houses, being of timber construction, are at
a bigger risk to things like dry rot in the frame and, because of this,
their longevity is in question.

Timber frame is not, in itself, a problem. You will find that most houses
more than 300 years old in this country are timber framed. Provided
ventilation and maintenance is good, timber framed houses can last a very
long time.

Christian.