My grandfather was X years old in the year X squared. In which year was he born?
For example if he was 33 years old in the year 1089 AD (= 33 x 33), he would have been born in 1056 AD - but then of course he would currently be nearly a thousand years old! You can safely assume that none of my family had children when they were very, very old, and I'm not too old myself.
Hint: In what year would have been 25?
A good starting point would be to find the age he would have to be if we were talking about 2010, and 2010 = 44.8 x 44.8 (approx). So our first guess is aged 44 in 1936 (= 44 x 44), which means he was born in 1892.
Just to double check the next possible age. He could have been aged 43 in 1849 (= 43 x 43) and born in 1806, which was over 200 years ago, and the question said that he didn't have children as a very old man.
A mother recently arranged a children's party and had 187 sweets to give out equally to the children.
Each child had more than one sweet and there were more children than there were sweets per child.
11 sweets each, for 17 children. 187 = 11 x 17.
You have the misfortune to own an unreliable clock. This one loses exactly 30 minutes every hour. It is now showing 4.00am and you know that is was correct at midnight, when you set it. The clock stopped five hours ago, what is the correct time now?