both surely are correct. 'sprightly' indicates an energy and vigour which are common but unexpected in old age. 'spritely' claims the old man is sprite-like (perhaps he moves via pixel-by-pixel relocation).
correct usage should not be allowed to block off interesting wongs in the language.
That's why I put it up. A newspaper described a politician in the UK (aged about 90) as 'spritely' and he complained about it. In his case, there is nothing elfin-like about him.
Ithink sprightly is right cause the old
man is inerjetic .
'sprightly' refers to the full of spirit and vitality makes his nature