Powell on friendship old and young

One thing I've been particularly enjoying this time through Hearing Secret Harmonies is when Nick Jenkins distills the fruit of his years of experience into general pronouncements on life. Like this one about friendship:

In any case the friendships of later life, as contrasted with those negotiated before thirty, are apt to be burdened with reservations, constraints, inhibitions. Probably thirty was placing the watershed too late for the age when both parties more or less begin to know (at least think they know) what the other is talking about, as opposed to those earlier friendships--not unlike love affairs, with all sexual element removed--which can exist with scarcely an interest in common, mutual misunderstanding of character and motive all but absolute.

The overarching point is hard to argue with, but at first glance Powell's explanation seems off: the friends of our youth we misunderstand? Seems wrong, no?

But with more thought, I found myself agreeing with him. When we're young and ill-defined, thinking taste more important than character, we tend to assume that anyone our age who has chosen a broadly similar approach to dress and affect surely shares our outlook on life--and the potent combination of our inexperience, ignorance of the world's multiplicity, and solipsism enables us to rush headlong into friendships that in later life caution would halt at the handshake.