Depends who you ask
Recommendations say age 60 now but ages 50-60 are when the most bone is lost so it would be good to know where you stand about age 50.
If you have been on oral steroids
for a long time or if your vit d level is low then you might need a scan even earlier. I do not agree that age 60 is the ideal age for a density scan but many doctors start at that age. I think the cat is out of the bag by then.