According to Official Guinness Records,
The fastest 50 m by a human wheelbarrow team is 14.87 sec and was achieved by Josh McCormack (the wheelbarrow) and Arjuna Benson (the pusher) (both Australia), at the Sports campus of Carey Baptist Grammar School, in Melbourne, Victoria, Australia, on 9 September 2008. During the same event, the record for the largest human wheelbarrow race was broken. Josh is 16 years old, and Arjuna is 15.
For a complete list of 2008 records, please visit 2008 Guinness Records in Australia.