I view one as needing to be at least 60 to be "old", and that is with the curses joke-hova placed on us. Even then, it is possible for someone to be 60 or older and in good enough condition to not be "old", as much as someone that is only 30 to be in such poor shape that they are "old". Physically, "old" is a condition where they are not regenerating but instead deteriorating. You reach this condition when most of your cells lose their telomeres to a degree where they cannot replicate or when your metabolism is so clogged with the poisons in our food, and lack the nutrients, so they cannot properly function.
Mentally, one can be "old" if they have a problem tolerating youth. Granted, the gangsta culture is objectively bad because so many petty crimes happen through this. Also, if one finds today's music lousy, there is an objective reason--they are controlled by someone that can't tolerate decent culture. Modern TV shows are also lousy, and because they lack substance and not because they are "dirty".
One is also mentally "old" if one feels guilty for having any fun. This is most common in the washtowel slaveholdery. Even teenagers can be "old" in this sense--I once ran into someone that was only 14 that hated music because it didn't glorify joke-hova (or jesus, as was the case with this devout xian). This trend runs through the whole washtowel--they can't enjoy anything without feeling so pious that they are willing to sacrifice it. From the ice cream money to that Led Zeppelin album (that even young people seem to find more entertaining than today's music), the washtowel makes people intolerant of having fun. And when you impose that on those around you consistently, you become an "old fogey" regardless of whether you are 6 or 120.
Supposedly, Satan is some 500,000 years old and has more appreciation for fun than a xian that is only 7. Old--definitely not, because I define "old" by how much time you have left compared to how much you already spent, or based on how much you are intolerant of people having a good time. For sure, being a devout xian makes you "old" before your time--and drains your energy so you become physically old before your time, too.