oldest

1. Of an object, concept, relationship, etc., having existed for a relatively long period of time.

   an old abandoned building;  an old friend

2. Having been used and thus no longer new or unused.

   I find that an old toothbrush is good to clean the keyboard with.

3. Having existed or lived for the specified time.

   How old are they? She’s five years old and he's seven. We also have a young teen and a two-year-old child.

4. (heading) Of an earlier time.
5. Tiresome after prolonged repetition.

   Your constant pestering is getting old.

6. Said of subdued colors, particularly reds, pinks and oranges, as if they had faded over time.
7. A grammatical intensifier, often used in describing something positive. (Mostly in idioms like good old, big old and little old, any old and some old.)

   We're having a good old time. My next car will be a big old SUV.  My wife makes the best little old apple pie in Texas.

8. Excessive, abundant.

noun

The oldest child in a family, or individual in a group.