In the summer between junior high and high school, I and a couple of friends decided to take up tennis. Our instructor looked youngish, but I doubt any of us paid much attention to that. So when, on the last day, we had a last group huddle, discussing how the classes had gone etc, he asked if we could guess his age, that immediatelly raised everone's suspicions. Sure, he was very tall, and rather big in general and, now that I'd inspected him more closely, he looked to be about 22, definitely not more than 25. So, people started guessing; 19, 23, 20, etc. Now, my own sense of humour often leans towards the dry wit side, so, disliking guessing games (they really do bore me), I went with 35. Deadpan.
He looked at me with a mixture of shock and not being sure whether he should take me seriously or not.
I can't remember if he ever did reveal his age.
But ... when school started up again after summer, and everybody's waiting outside the auditorium, who do we spot, but our very tall tennis instructor! And, as it turns out, one of our other friends knows him, revelaing that not only will we be sharing classes with him, but he's actually a year younger than us.