The age that you start feeling old is usually by age 40 to 43 and above.
However some people older than 40 feel younger and not old so it can vary depending on the person.
I'm 35 and will be 36 in a few months some days I do feel old and other days I feel younger.
However by age 42 most people do start noticing physical signs of aging.
I've known people in their 80s and 90s that say they feel young as 20s to 30s as they stay very active.
And then I've known people in their 30s and 50s that say they feel like they are in the ages of 70 to 80 or older.
So it can depend on the person.
Signs of aging like wrinkles and spots are the results of the accumulation of defects in cells and intracellular structures.
Experts have found that skin aging typically starts around age 25.
According to the World Health Organization, aging is commonly measured by chronological age.
As a convention, a person over age 65 is often referred to as elderly.