「覚えていない」は、そのまま I don't remember をよく使うと思います。
「はるか昔のことだから」は、いろいろ言い方があると思いますが、簡単に言えるのは it's ages ago だと思います。
ages は、非常に長い期間のことを指し、ages ago で、「ずいぶんと前、はるか昔」を表します。
for ages とすれば、「ずいぶんと長い間」という意味になり、例えば、次のように使えます。
I've been waiting for ages...
（ものすごく長い間、待っているんだけど...）
お役に立てれば幸いです。
こんにちは。
・I don't remember because it was so long ago.
「すごく昔のことだから覚えていない」
・It's too long ago. I don't remember.
「昔すぎる。覚えていない」
上記のような言い方ができます。
so long ago は「めっちゃ昔」で too long ago は「昔すぎる」のようにちょっとだけニュアンスが異なります。
ぜひ参考にしてください。
If you are wanting to explain something happened a while/long time ago then you can simply say 'It's too long ago' or 'It's been so long' these both mean the same thing
If you don't remember it means you have forgotten and can't tell them what it was
ずっと前に起きたことを表したいなら、'It's too long ago'や'It's been so long'と言えます。どちらも同じ意味です。
'I don't remember'は「覚えていない」「忘れてしまった」という意味です。
The word "anymore" helps to say that once you could remember but not now. "Long ago" helps explain that it has been a very long time since you were a child. I hope that this helps :)
I have no recollection of Christmas presents received as a child
My memory fails me!
If your 'memory fails' you then you simply cannot remember or recall something. If you have 'no recollection' then you have no memory of something - perhaps it happened - or perhaps it did not. In the first example sentence above, it could be you were never given any presents as a child! Or you may have just forgotten all about them.
My memory fails me'は「思い出せない」という意味です。
'have no recollection'は「全然覚えていない」という意味です。上の一つ目の例では、もしかしたら一度も子どもの頃プレゼントをもらったことがなかったかもしれません！あるいは、単純に忘れてしまっただけかも。
So' in this case is used in the sense 'very'. 'I have no clue' is a common phrase to say 'I have no idea' or 'I really don't know. 'It was ages ago' indicates it was many, many years ago. It's important to use the past tense verb 'was' in this case.
この場合、'so'は'very'（とても）という意味で使われています。
'I have no clue'はよく使われるフレーズで、「全く分からない」という意味です。
'It was ages ago'は「大昔」という意味です。この場合、過去形の'was'を使うことが大切です。
Here are two sentences that we can use to describe this idea. Notice that they are very similar in structure but simply have pieces of the same information moved around with either, "I can't remember," being at the beginning or, "to remember," coming at the end.
You can use any of the above two sentences to tell someone that you cannot remember a specific thing because it has happened so long ago.
Example;
A; Do you remember getting a file from him?
B; No i can't recall it, it's been a long time.
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