Answer:
For humans, old is usually when you are 2/3 through your expected lifespan. Subjectively, someone can be "old" if they are part of an earlier generation. (To kids, all adults may seem old.)
For things, a person may consider them old when they are obsolete, or when they were built or constructed before he or she was born.
Scrmrz: To me, i don't really think any age is old. lol probably cause i counted to 1,000 when i was 7 don't mean to brag seriously, but in my opinion i don't really think any age is old, but that's just me, pretty much nothing scientific going on. Some people might consider themselves as old when they experience health problems at an age they feel is old.