In all other aspects of the rules the SN uses the PDGA rulebook except for the age criteria.
(every other sport on this planet classifies masters as 40 and gmasters as 50)
It should be determined by the year of the event-- in comparision to the date of birth of the old guy in question...
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CLASSIFICATION OF PLAYERS 804.08
( [
pdga.com] )
(2) Master: A professional division available to players at least 40 years of age in the year the tournament begins.
(3) Grand Master: A professional division available to players at least 50 years of age in the year the tournament begins.
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As far as your question "are TD's suppose to let people play in these divisions because they played there in the last tournament they played?" ....
Perhpas Jimo can better answer that for you.