Question for runners who are gradually turning into swimmers

Okay, so part of this might be aging... In my 40s and 50s, I could count on running 8something pace in a race (in fact, my 10k best was 48:40, but that was quite a while ago). In my early 60s, I faded to 9something. Now.... sheesh! 10 min. miles are race efforts! And that's just for the 5k! For the 10k and beyond... 11 is getting to be the new normal and 12 is peeking out from behind the curtains. Yesterday, I ran a 10k race (overslept and missed swim practice, so needed some kind of workout... that's what I get! Still, I was happy to support the race as it's in memory of a friend who passed away a few years ago). I finished LAST! Granted, my time wouldn't have gotten me in last had the weather been warmer and attracted more people. When it's 15 degrees in the morning, you get mainly the diehards. :) I did around 72 minutes and, especially later in the race, that pace hurt the way sub-8 used to. At times, I yielded to the temptation to walk, but I didn't want to give up. Still, I was getting more and more discouraged as I continued. Meanwhile, my swim times, while lately not significantly improving, do occasionally show nano-second advances, and I don't seem to be slowing down. I won't say they're fast--they've never been, but a recent 200 freestyle was a personal best, albeit by less than a second. ;) And that was with a sore shoulder. It seems harder and harder to get started running and pace gets slower. I've come to like track workouts, especially short sprints such as 200s b/c I can feel fast if only briefly. But even then, times have slowed down, though not as much. Part of this is that I don't run as frequently now as I swim--and when I swim, it's pretty much always in masters' practice with my wonderful, merciless coach. :) So I'm swimming maybe 4-5x/wk, running about 3x/wk. So, those who both swim and run--can a person have it both ways? I am signed up for a 10 mile race in early May. And though I was slow in the 10k the redeeming feature was that it gave me a supported distance run. I have a 7 mile race next weekend--entering more for the distance than any time goal (although hoping not to be too, too frustrated w/ speed... in fact, I may deliberately make it a run/walk, not even have my watch running). I might decide though that swimming is becoming my main sport and running is the alternative cross-training workout when time or circumstance won't allow swimming. It's beginning to feel okay for me to decide that, but curious as to how/whether others experience a similar transition.