Here's my entire list, which I suppose includes both progression and regression.
Age 22: 2:39:56
Age 23: 2:33:36
Age 24: 2:30:03; 2:23:37 (Boston, so not record-quality, but a reasonable reflection of my fitness at the time, following a period of several solid months of training)
Age 29: 2:28:++ (first marathon in almost five years, after a long period of little running or racing of any sort; ran the majority at sub-2:20 pace and walked much of the last two miles)
Age 30: 2:20:45; 2:19:31; 2:20:01 (all three within a ten-week period, the last was a sub-66 first half followed by a 74+ second half, which included some combination of running, limping, walking, and worse)
Age 32: 2:18:54.5
Age 41: 2:28:53
Progress came almost entirely from increasing volume and, perhaps to a lesser extent, intensity. Apparent plateaus in finishing times (particularly during my early 30s) were probably less a reflection of plateaus in ability than increasingly aggressive (and ultimately unachieved) goals and ill-timed injuries. I hoped to nail at least one really good race, but, for various reasons, that never worked out. My last marathon, at age 41, was a one-off attempt to see if better living, working, and training schedules could get me back to a good level of running (unadjusted for age), but I discovered that age and years away from the sport were too much to overcome, and it just didn't feel the same. That last marathon was almost twenty-five years ago. These days, I stay in reasonably good running condition (for a guy over 65), but it's hard to justify training for time or competitive goals; there's just too much else to do in life, which now seems too short.
As for your original question about talent versus grinding, I'm ambivalent. I had an extremely undistinguished running career in high school and college, but perhaps I had a specific talent in responding to my own very quirky (and pretty darn hard) training methods, which developed over years and without any coaches or training partners.
Laying all of this out causes me to rethink the eternal question of whether it was all worth it. For me, I think it was, but running has often been the most enjoyable and straightforward part of my life. And it still is, even as my reasons and motivations for it have evolved over the decades.