Decline - what decline? Haha
TLDR - If you don't start running till your are an older runner, newbie gains can postpone/delay the inevitable...
Currently 56 years old and almost every race I have run has been a PB and in training runs I am able to go farther and faster with more frequency.
After never running competitively, or not more than for a couple weeks every few years, I decided to bucket list a marathon. Basically I fully embraced running as something I wanted in my life in January 2016.
I figured I would run for two or three years before attempting the marathon, but to measure where I was at, I decided to try a half marathon in March of that year. I ran with a local club targeting a 2 hour half and probably averaged about 25 mpw from Jan-Mar.
3/2016 - Half @ 1:54:34 (PB)
Didn't with run with much regularity the rest of 2016 and into 2017. Started a more regular pattern of running towards the end of 2017, usually anywhere from 15-30 miles per week. No real plan, just running mostly by feel, although I did track my runs on my phone using Strava.
10/2018 - 5k @ 20:51 followed by a 10k @ 45:46 (both PBs)
12/2018 - Half @ 1:40:01 (PB)
At the beginning of this year (2019) I targeted a fall marathon so I started running with a bit more purpose. I even bought a running watch and eventually a chest strap to more accurately log my times, pace and heart rate. Averaged about 25 mpw starting out and topped out at 55 mpw a few weeks before the marathon, although I did have to take most of June and part of July off due to a stray dog using my calf as a chew toy during one of my runs.
7/2019 - 5k @ 21:35 (wasn't really in shape due to holes in my calf, but was still pleased with the result - it was HOT!)
8/2019 - 5k @ 20:28 (PB)
9/2019 - 5k @ 20:51 (it may have been hot, but at least it was humid. haha)
9/2019 - 30k @ 2:21:19 (PB)
10/2019 - 5k @ 20:08 (PB)
10/2019 - 5k @ 19:55 followed by a 10k @ 44:02 (both PBs)
11/2019 - Full @ 3:15:52 (PB)
12/2019 - Half @ 1:32:17 (PB)
I don't follow a training plan, just run far, fast or sometimes far & fast (with fast being relative for someone my age). Although I use electronics to log my stuff in Strava, I always run based on how I feel, often not knowing which route I am going to take (i have lots of options once out from my front door), or how far/fast i am going until I actually do a warm up jog of 10-15 minutes. Someone I run with on occasion told my I probably run my slow runs to fast and my fast runs to slow, but whatever I am doing seems to have worked for me so far. I can't say exactly when, but some where in Sep/Oct all my training runs just seemed to get easier and recovery times got shorter even though I kept increasing pace and mileage each week. As I am writing this post I am thinking its probably due to the track work I started doing, and/or from the cooler fall temperatures (more likely?).
Anyway, the recent full and half were real close together (two weeks) so I've shut it down for the most part to give myself a chance to recharge before starting up again in January.
I still feel have a bit of room to progress before I plateau or any age related regression starts moving my times in the other direction.
It's probably a reach, but I definitely think I am capable of a sub 3 marathon. My optimism got the better of me so I went and purchased Jack Daniels v3 in an attempt to come up with some type of plan to get there.
Regardless, even if I never run any faster then what I did this year, I plan to continue enjoying my time on the roads and trails for as long as possible.