There is a difference:
Everlasting= no beginning, no end
Eternal= beginning but no end.
Not according to the Oxford dictionary.
Eternal
1. a.A.1.a Infinite in past and future duration; without beginning or end; that always has existed and always will exist: esp. of the Divine Being.
Everlasting
1. a.A.1.a Lasting for ever; infinite in future duration; endless;
That said they have equal duration. Infinite.
Not exactly true:
eternal has infinite past + infinite future = infinity + infinity = 2x infinity
everlasting has infinite future = infinity = 1x infinity
Of course you can make the argument that 2x infinity = infinity, but the math is not that easy... 
of course if you search the usages in the scriptures there is no consistency in the translation of the two. You will find eternal and everlasting interchangeably used along with forever to translate the same Greek word in different verses- and sometimes even within the same verse.
And these shall go away into everlasting
G166 punishment: but the righteous into life eternal.
G166 (Mat 25:46)
The point is moot therefore, because the word olam (Hebrew)was translated aion(Greek). Olam was a word used for a variety of indefinite conditions of time and world, meaning "unkown" or "unknowable" or "other-wordly". That is why aion gets translated age in someplaces;world in others;forever,eternal,everlasting in others- the actual meaning cannot be defined without context.
When connected through context to God it means transcending time forward and backwards. When used with the future lives of the redeemed it means forward everlasting. When used of those who go into the lake of fire it means until they have "paid the last penny" i.e., bowed the knee and confessed with their mouths Jesus Christ as Lord to the glory of the Father.
"For this reason God has given Hom a name above every name that at the name of Jesus Christ every knee shall bow and every tongue confess......:o)
