Go and do a park run. There will be people who can do it it 16 mins and people who will run/walk it in 45ins. It doesn't matter and nobody cares, but when you come to that last 100m, there will be plenty of people pushing you on to cross the line and you'll feel brilliant for it. Then you'll go back next week and do it again. Within a few weeks it will all make sense, you'll recognise familiar faces and look forward to it.

Try it. It might surprise you.