WordNet records no synonym and no antonym for elder statesman. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
any influential person whose advice is highly respected
an elderly statesman whose advice is sought be government leaders
Synonyms, antonyms and the broader and narrower relations for elder statesman come from Princeton University’s WordNet. Full sources and licences.