How Crazy Is This?

Just to give everyone an idea how delusional I really can be: at 47 years of age I keep on thinking to myself, that with just a bit more training and technical improvements, I can start catching the age group swimmers that train at the same time as I do in the early morning. Here I am, just passed the half way point in my life and I am still catching myself doing the "next year is my break-out year" thing. Crazy. Anyway here is a couple of questions to the great crew here with regards to training: Anybody out there in the 45 to 50 zone who keeps a training log and would be willing to share it with me? I have absolutely no idea what other guys my age are logging per work-out and week and what would be considered decent pace times. I am currently training mostly short-course meters, but I will be training long-course yards (bizarre old out-door pool) for the next two months. I can manage to hold 1:15 repeats for up to 10 by 100 right now, but my goal is to get that down to 1:10 or 1:05 by summer's end. I want to go like I did when I was eighteen just for a few moments. How about underwater training? I have really poor anaerobic tolerance; I practically have to breath every stroke (versus the common every second or third). An old acquaintance of mine told me of a Navy Seals session he watched years ago where the SEALS had spent an entire 90 minute session swimming lengths under water to build up endurance. Any value for a swimmer? My lack of tolerance probably explains why I was originally a backstroke specialist when I was a kid. Sprints. I have taken several member's advice and added numerous sprint sessions to my work-outs now. I am doing them sproradically now since I do not have any meets on the horizon, but I intend to ramp up the speed work as the fall competitive season approaches. One person suggested I keep everything down to 25 meter full out efforts while another suggested that I needed to get my 100 meter repeats down under 1:10 if I was going to meet my 400 meter goal of sub 5 minutes. Do I mix and match? Where do I put my emphasis? BTW: this site is fantastic.