weird question about elves

[Luinëcolloien]

Well in the books, Elrond, Elladan, and Elrohir were all described as looking 'niether young, nor old' (or something of that like.) So I take this to to mean that they were all quite old but being Elves made them just quite not look it. Or, something else I thought of, which is probably not right but, Galadriel is universally taken to be very fair and youthful looking, correct? Nothing about her looking young nor looking old. Do you think that Elrond, Elladan, and Elrohir looked that way because they were not 100% Elf? Maybe Elrond looking that way had something to do with only being half Elven and same with the twins, being 3/4 Elven. Well, I'm straying off topic, so I should stop now. Thanks.