I had a lot of fun with Ian, I have to say :D He's a little more grown-up than Ianto, I think, in some ways, and also a little more open.

I seem to recall reading somewhere in an interview that the Torchwood writers believe that the average lifespan for a Torchwood agent is 35. Apparently they were originally going to kill Ianto instead of Owen in the finale, but Burn Gorman had other projects he wanted to do, or something.