Is there an English way of saying that you don't feel like thinking how long ago that really was, Pat? The German "Jährchen" expresses both a slight sense of humour and also affection. Something along the lines of "a good few years ago", which BTW would not work because it pushes the event too far into the past?

Oh, those diminutives and their connotations.
We have three different diminutives of 'год' (year), but none of them is/are an exact fit. xD (one is a sweet, baby-style diminutive [but Tom and Mary aren't likened to babies here], one is somewhat rough (light irony, maybe, a bit of jest), one combines the previous two).
Do you think the slightly jestful one could do?

Slightly jestful is exactly what it is.

Good, added it.
Good thing that, for once, there is a good fit. These things are notoriously complex to translate properly.

>"a good few years ago", which BTW would not work because it pushes the event too far into the past?

In that case, these three won't suit.

Tom and Mary have been married for yonks.
(Yonks - British informal - = for a very long time)
or
Tom and Mary got married ages ago.
Tom and Mary have been married many a year.

what about:
Tom and Mary got married a few years back. ?

I can't think of anything else at the moment. I can't think of any humorous English usage of "a few years ago / for a few years".

Most dictionaries just have "year" for Jährchen and dict.cc doesn't have it listed at all!!

I'll think about it (and would welcome any suggestions)!