If you run the London Marathon next year and finish in 4 hours, brilliant. If you finish in 6 hours, also brilliant. The only “bad” time is the one where you don’t finish at all, or you quit because you thought you were too slow. Don’t compare your chapter one to someone else’s chapter ten.
And here’s a little secret: years from now, you won’t remember your exact time. You’ll remember the crowd shouting your name, the blister on your foot, the stranger who gave you a jelly baby at mile 20. That’s what the average time can’t measure. So go for it—crawl, walk, or run. Just make sure you cross that finish line with a smile, and maybe stop for a roast dinner after.