I can see some weight gain due to higher muscle mass into your mid 20s. After that you should stay the same weight or less.
I have dogs and keep them trim. With age they get lighter. Their muscle mass goes down with age after they reach adulthood. This is true for horses cows etc.
Like others have said, just because the stats say it is a fact doesn't mean it is normal, leave alone healthy! That includes athletes. Look at George Foreman ...
George