I think I can be effective til I'm like in my 60's. After that I will just be too slow up and down the court. I will have lost my ability to defend effectively by the time I'm 40 probably because already right now quicker people give me fits.... but hey as long one can rain, make smart decisions, give what they have... a person could play for a long ass time.
Oh and don't get fat. That's probably the biggest kicker