We have the birth certificate of his son Walter (my g-grandfather) dated 1890 (father Theophilus Jones, mother Elizabeth Jane Jones, formerly Uglow). He was in East Stonehouse, Plymouth on the 1891 census with wife, stepdaughter (Annie Lititia Walker), daughter Elizabeth Ann and son Walter. He is in the same place in 1901 with Walter and daughter Esther Mary (I can't remember if the older daughter is there, but Annie has gone). Annie was born in Kent in 1881 and Elizabeth was 1888 so I presume they were married between those two dates (although not necessarily...) I found A Theophilus in Carmarthen St Peter in 1881 (aged 18) and I just have a feeling about him. That's the one who was supposed to have been born in Llanfihangel Aereddia. I can't confirm that he is the right one, of course, but he was the most likely candidate of all the records I found in the 1881 census (we have disks from the Church of Jesus Christ of Latter Day Saints).
Cas, the one with father Walter would make sense if he called his son Walter... That was quite a common thing. I think 1867 would be far too late. 1865 is possible, but something about it doesn't strike with me. On his death record (military, 1916) his age is given as 52, if I recall correctly. I reckon he hadn't had his birthday yet when he died. I favour 1863, although that could just be myself leading me the wrong way
I'll go to the military board now. Thanks!