My first run was on January 23rd when I ran 3.8m, so 5km-and-a-bit. I only did that distance as I was determined that regardless of how slow I was, I would not run less than 5km! I almost certainly didn't have your level of base fitness.
Looking at my Strava log, I ran the same distance a further six times over the following two weeks before starting to up the distance a bit with a longer Sunday run. On April 5th, around 10 weeks after I started, I ran my first half-marathon distance and my pace for that (9:42/mile) was significantly quicker than my 3.8m run in January (10:40/mile).
I think most of us who are relatively new to this will testify how quickly your body can improve, both with regard to distance and speed, if you stick with it.
