What is the difference between 'eldest' and 'oldest'?

I would think that eldest would have to do with the firstborn: the offspring who came first in the order of birth, and that the oldest would be concerned more with non-living or living things other than humans. But, maybe someone else might have a more precise idea though.

Thank you, CLough, for your prompt answer.

'Eldest' does have to do with family, or perhaps, a specific group of people, while 'Oldest' would refer to a generic group, or as you stated, non-living things.

Thank you, CLough, for your prompt answer.

'Eldest' does have to do with family, or perhaps, a specific group of people, while 'Oldest' would refer to a generic group, or as you stated, non-living things.

You are welcome for the answer! I hope that it is helpful to you!

Oldest:

A superlative of old.

Eldest:

First, either in age or seniority

http://encarta.msn.com/encnet/features/dictionary/DictionaryResults.aspx?refid=1861607748

Greatest in age or seniority.

http://www.bartleby.com/61/92/E0069200.html

Noun: the offspring who came first in the order of birth
Adjective: first in order of birth

http://www.rhymezone.com/r/rhyme.cgi?Word=eldest

http://lookwayup.com/lwu.exe/lwu/d?s=f&w=eldest

If there are four brothers and the first born is dead, the second
One is called the oldest among the brothers. He can never be
Called eldest among the brothers.

Eldest is the name of a book by Christopher Paolini. In the book, the eldest is the senior dragon, like drogon that was born before the others.
(I hope it helps)