As I recall it was somewhere in the early 1870's. I was twenty-three at the time. There's a reasonable account of the event in Untold Tales #83 they tell me.
> Did he get his other minor cosmic items around the same time, or later?
All part and parcel of the keeper of the Chronometer package, old chap, so all at once.
> When was the Mumph knighted?
Well now, let's see. Knight of the Order of the British Empire (KBE) in 1871, Knight of the Grand Cross of the Most Honorable Order of the Bath (CGB ) in 1892, Knight Grand Cross of the Royal Victorian Order (GVCO), in 1900, Knight Grand Cross of the Most Distinguished Order of St Michael and St George (GCMG), in 1927, Fellow of the Royal Society 1903 - hence the suffixes
Mumphrey Wilton KBE GCB GCMG CGVO FRS. Then there were a few medals like the Victoria Cross and bar and the Distinguished Service Order. Old news now. Could add a few more letter for them, but what's the point? It's all swank.
> What year did Mumph join the League of Improbable Gentlemen, and how old was he at the time?
Joined not long after gettin' the Chronometer, I remember that much, in the early 1870s.