The problem with Jon being younger than Geoff, though, is that they talk about their past as if they were fairly close contemporaries. Although we're not given an age for Geoff until rather later in the series, his rank in the Navy and Giles's age suggest that he is likely to be in his mid-forties at least. I think the obvious answer is that Forest was nodding, and it's not terribly important anyway, but thinking up scenarios to cover inconsistency is a good game.

Geoff's envy suggests there weren't many people between him and ownership of Trennels when he was 18, I think: if he had a bunch of elder brothers or Jon younger ones, him inheriting would always seem very remote and I don't think it would quite have reached the pitch of 'barely being able to be polite to him.' The difficult feelings seem to arise from being heir presumptive.

I agree about Peter and Nicola: I think he slopes off under his own initiative to intercept her rather than being sent, or even, perhaps, has just slipped off to be alone (he tends to seek solitude when upset), and half-consciously wanders the way she's coming home.