Elves live for a very long time and change very little

Legolas stirred in his boat. ‘Nay, time does not tarry ever,’ he said; ‘but change and growth is not in all things and places alike. For the Elves the world moves, and it moves both very swift and very slow. Swift, because they themselves change little, and all else fleets by: it is a grief to them. Slow, because they need not count the running years, not for themselves. The passing seasons are but ripples ever repeated in the long long stream. Yet beneath the Sun all things must wear to an end at last.’

The Fellowship of the Ring, Book Two, Chapter 9: The Great River.