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1.
a hipster/scenester usually 30+ years of age that hasn't accepted the fact that developmentally they should be beyond trendy clothes and fashionable elitist attitudes.
look at the Emo haircut on that oldster! skunk spots are fab, but taupish mops are not!
by mike weird November 02, 2006
 
2.
A person who has transitioned from adulthood into Olderhood . Part of the “Now Generation” oldsters have a desire to live life to the fullest, travel, meet new people, exercise, eat healthy, and incorporate a little bit of silliness in their lives. If youngsters have youth and dreams, then oldsters have age and wisdom. In this age of information, oldsters live in defiance of their advancing years and continue to crave new ideas and experiences, and have an insatiable thirst for learning.
In a classic oldster move, my neighbour decided to learn Spanish at the age of seventy.
by sebtbear June 30, 2013
 
3.
1. One who is not just old, but is so old that he/she has basically make a name for themselves by being old; They have made being old seem cool.

2. A slang, rude nickname for one that is old, but does not make it cool; In this case, their oldness is the cause of their downfall.
1. That oldster is 113 years old.

2. That oldster gave me a 15 page essay due tomorrow.
by The Jimmynator September 17, 2003