He charges $30 an hour for he and his buddy he brought on. So if by himself he could get it done in less than an hour he’d probably go with $20.
But he and his buddy target each making $15 per hour and most lawns they have take them 1 hour or more. They do mow, edge, trim, and blow.
So for just mowing and it taking them less than an hour they would likely ask for $20. Maybe $25 if they had to drive a bit to get to you.
So for some kid in your neighborhood, I’d say $20 if it’s just mow and only takes 50 minutes.