The race to which this being belonged - if any - is a difficult and unresolved question. For a fuller treatment of this issue, see the entry for Tom Bombadil.

In general form, iarwain looks to be translatable as 'oldest', and indeed the phrase 'Iarwain Ben-adar' is apparently translated by Elrond as 'Oldest and Fatherless' in the text of The Lord of the Rings (in The Fellowship of the Ring II 2, The Council of Elrond), so a meaning of 'oldest' seems a natural assumption. However, Tolkien himself gives the meaning as 'old-young', so perhaps Elrond was concerned to give this unusual term a straightforwardly comprehensible translation, rather than straying into the explanation it would otherwise have needed.

The Elvish prefix ben- means 'without', and adar is 'father', so the name 'Ben-adar' literally means 'without a father'. Variants of the adar element of this name is fairly common in other names, too. It appears as atar, for example, in Ilúvatar 'father of all' and Atanatári 'Fathers of Men'.

Elrond was born shortly before the end of the First Age, and there's no record of his having passed east of the Blue Mountains until after the end of that Age. Most likely, he encountered Tom in the early Second Age, before the great forests of Eriador had been felled by the Númenóreans. So, when he recalled meeting Iarwain among those woods, he was thinking back to a meeting that took place (very roughly) 5,500 years in the past.