The are many other units of time, the month, the second, the fortnight etc. The way powers of ten work for each unit of time, there is a unique power of ten 10-to-the-nth so that 10-to-the-nth units of time is between 10 and 100 years. For example 100 months is 8 1/3 years (less than 10 years), 1000 months is 83 1/3 years (between 10 and 100) and 10,000 months is 833 1/3 years (more than 100 years). So for months, 1000 months is between 10 and 100 years. Many more people can celebrate their 1000th month birthday, then their 100th.
This gives several "party opportunities" for people between the ages of 18-33. (Like celebrating a 1000-month birthday, only that would be for someone 83.3 years old.) What are they? Answer