Yes, Frank. That about sums it up.
Am off to the Local Studies Library tomorrow (yes, it is open on a Saturday morning) to see if I can glean any info from his marriage certs. I know which church the 1930 one was held at and am hoping that would give his age and father's name. Not exactly sure where in Derby his 1918 marriage was, but I know where the bride's parents were living in 1911 (and same address in 1901 for that matter) so I'll start from that parish and see where it leads me.
The 1911 census I found for a John Rowlinson (b. 1896 in Foxt, Staffs), living in Derby, a tailor maker, is him, I think - because he's listed as nephew to the adults in the house (Alfred Wood and wife Caroline Elizabeth) and I've found a Caroline Elizabeth Rowlinson (b. 1865 Ramshorn, Staffs) who married an Alfred Wood. I've found Caroline on a couple of census records, with her parents (Robert and Mary), but no mention of a brother John (supposedly father of the chap in the photo).
Edited to say: I've just added the 1911 census into to my tree and Ancestry has thrown up a death record for a John Rowlinson in Derby in 1970, which gives a dob of 10 May 1894. Someone up-thread said they needed a dob for elimination purposes, so am hoping that helps (assuming it is the right chap, of course).