Craft exercise old boy's taken up (6)
I believe the answer is:
pedalo
'craft' is the definition.
(I know that pedalo is a type of boat)
'exercise old boy's taken up' is the wordplay.
'exercise' becomes 'pe' (Physical Education).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'boy' becomes 'lad' (informal term for boy).
'taken up' says the letters should be written in reverse.
'o'+'lad'='olad'
'olad' written backwards gives 'dalo'.
'pe'+'dalo'='PEDALO'
(Other definitions for pedalo that I've seen before include "Pleasure craft -- old ape (anag)" , "Foot-operated boat" , "Boat driven by foot power" , "Type of pleasure boat" , "Man-powered leisure boat" .)