Returning to Geoff’s British census data, in 1901 Eric’s younger brother Mervyn was 11 having been born in Geelong, Australia in 1890. It follows that the family must have left Australia between 1890 and 1900, when Eric was between 6 and 16 years of age. So, before the age of 16, it seems that he had become “a well-known steeplechase jockey….and had sustained a bad fall whilst racing in Australia.”
In summary, Eric Langden must have had his fall when he was either in his sixties or in his early teens. Neither seems to make sense. So what’s wrong?
I'd been musing on that too, Tony. In fact, the entire Longden family appears on the 1891 census as well. In Hove, where they are all listed as "boarders" at the establishment of John Darbyshire at 1 Wilbury Rd. So young Eric left Australia some time shortly after the birth of his brother Mervyn Irvine Longden in 1890.
The name Longden seems to be not unknown in Geelong, since in 1875 there was a trial involving a Captain Duncan Longden - possibly Eric's grandfather? - regarding a forged promissory note for £110: he was acquitted. However, Eric's father Edward seems to have operated his gold mining business out of Melbourne and had been to Britain at least once before - there's a record of Mr & Mrs Longden and family returning from Plymouth in October 1888.
Eric's brother Mervyn served in the Royal West Kent regiment in the Great War, rising to the rank of captain. There's a note on his army records from about 1920 that all correspondence should be sent c/o Standard Bank of South Africa at Potchefstroom. So we perhaps have another (or the same?

) South African - and gold mining? - connection ...
As for Eric's father - he filed for bankruptcy in London in June 1902.
So I supect the "jockey" story is - frankly - hogwash. Probably not intentional, but - to quote The Bard slightly out of context:
"Old men forget: yet all shall be forgot,
But he'll remember with advantages ..."