The age distribution, , in Altnau is; 199 children or 10.0% of the population are between 0 and 9 years old and 295 teenagers or 14.9% are between 10 and 19. Of the adult population, 193 people or 9.7% of the population are between 20 and 29 years old. 247 people or 12.5% are between 30 and 39, 395 people or 19.9% are between 40 and 49, and 277 people or 14.0% are between 50 and 59. The senior population distribution is 222 people or 11.2% of the population are between 60 and 69 years old, 104 people or 5.2% are between 70 and 79, there are 45 people or 2.3% who are between 80 and 89, and there are 4 people or 0.2% who are 90 and older.