Training youth upset old boat (6)
I believe the answer is:
pedalo
'boat' is the definition.
(I know that pedalo is a type of boat)
'training youth upset old' is the wordplay.
'training' becomes 'PE' (Physical Education).
'youth' becomes 'lad' (lad means a young man).
'upset' is a reversal indicator.
'old' becomes 'o' (abbreviation as in OT - Old Testament).
'lad' backwards is 'dal'.
'pe'+'dal'+'o'='PEDALO'
(Other definitions for pedalo that I've seen before include "Type of pleasure boat" , "Foot-powered pleasure craft" , "Small pleasure craft driven by paddles" , "Man-powered leisure boat" , "Pleasure craft -- old ape (anag)" .)