Very old, and swimming in Tyne (6)
I believe the answer is:
ninety
'very old' is the definition.
(I've seen this before)
'swimming in tyne' is the wordplay.
'swimming' is an anagram indicator (letters swim around into a new order).
'in'+'tyne'='intyne'
'intyne' anagrammed gives 'NINETY'.
'and' acts as a link.
(Other definitions for ninety that I've seen before include "old age" , "Number of degrees in a right angle" , "high number" , "Figure in inn, yet, strangely" , "XC (in ancient Rome)" .)