Enter a race!
Enter a race!
Enter a race!
Enter a race!
Enter a race!
Enter a race!
Maybe a 5km or at most a 10km. There are plenty around - try
Runners World Event Search or the event listing Admin provides here?
Race your heart out. Get a PB
Then take a month or two more of training and then.........
Enter another race! Beat the PB.
Then....
(I don't think I need to tell you, do I?) :-)
Racing will give you something to aim for - and (before you ask) there will be many slower, fatter, older, less fit people in that race than you!
Do it!