I don’t know if I even qualify to be an AOS, because I rarely swim 
Anyway - I started tri’s three years ago and had not been to the pool for ten years. I never swam as a kid, except for the kind of swimming we did in school (which is closer to taking a bath than swimming).
My swimming happens the last 1-2 months before Tri-season every year. Last year I totaled about 25 000m for the year So far this year I’m at 4200 m 
When I first started out I would be swimming around 2:00 pr 100m SCM, and be able to hold that pretty steady. Three years in with way to little swimming I start the season by swimming some 200/400m repeats at around 1:40/1:45 pr 100 - LCM. (and that pace is where I am at now). Last year, after a short swim-period, I maxed out at 6:05 for 400 LCM, but so that around 1:40pr 100 LCM was my “steady” pace in the pool. I find very little speed advancing from “steady” to “hard” swimming… a 1:40 100m LCM feels quite leisurely, but a 1:30 feels close to max. I could probably sprint a 1:20 LCM fully rested (start with kick of wall), but no faster. PR for IM swim (wetsuit) 1:02 last year. Fastest HIM swim just over 30min. Open water is same feeling as pool - I can go pretty comfy around 1:40 give or take a few sec, but I cant for the life of me speed up more without sprinting and dying in 100m.
Hopefully I’ll get to this level or a tiny bit faster this year.