Possible Clues:

• ` `You can't teach an ... ... new tricks' '
• Proverbial nonlearner
• New tricks non-learner
• Slow learner?
• One who's past the age of learning, in a saying
• Unlikely learner of new tricks
• ''You can't teach an ... ... new tricks''
• You cannot teach an . . . . . . new tricks''
• Too beastly ancient to be receptive of 27 across
• ''You can't teach an . . . . . . new tricks''