Restless type able to swallow date, say, upside down (6)
I believe the answer is:
fidget
'restless type' is the definition.
'able to swallow date say upside down' is the wordplay.
'able' becomes 'fit' ('fit' can be similar in meaning to 'able').
'to swallow' indicates putting letters inside.
'date' becomes 'd' (common abbreviation eg in DOB, date of birth).
'say' becomes 'eg'.
'upside down' shows that the letters should be reversed in order.
'eg' in reverse letter order is 'ge'.
'd'+'ge'='dge'
'fit' enclosing 'dge' is 'FIDGET'.
(Other definitions for fidget that I've seen before include "Move restlessly" , "Squirm" , "Restless person" , "Wriggle" , "Make small movements through nervousness or impatience" .)