Any sports activity depends on physical fitness,tenacity of mind, but it varies from person to person .There is no line of demarcation of age.Retirement is inevitable in any activity---In any service-the age limit is 60 yrs.But in sports it may be extended till 50 yrs as a coach,commentators etc-as per his/her physical and mental fitness.
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Not just sports every art form has a stage life. Whether one is an actor, singer, dancer, etc there comes a time after which it is not possible to perform in the center stage. It does not mean they become totally useless after achieving their peak. They can always take up a role in the backstage. A sportsman who is no longer fit to play in the national level can still continue to play in the state level for some more time and then if he is still interested in the sport can take up the role of a coach, referee, or can serve the sport in some official capacity.