So, Chronicles points out the Night elves were made virtually immortal in addition to highly intelligent by their transformation from Dark Trolls to Night Elves. Other perks gained were enhanced strength, stature and dark skin.
how long is virtually immortal? - compare that to when they are linked to Nordrassil they are said to become immortal.
My conclusion here is Night elves are permanently virtually immortal - but this is not true immortality, it just means they live a very long long time - my estimate would be something like 15k-20k years. This along with the enhanced intellect, strength, stature and skin are permanent.
When they were linked to Nordrassil, that Nozdormu blessed, they actually became properly immortal, so it's like aging which was already much slower in them than other species, was frozen. It's like the blessings of Nordrassil preserved their psychie (Ysera's blessing), their bodies (Nozdormu's blessing) and their lives (Alexstrasza's blessings) in time. They lost that in WC3.