If only I could extend the end of my chromosomes, I could become young again.
ご質問ありがとうございます。
"If only I could extend the end of my chromosomes,"＝「私の染色体の末端を伸ばすことが出来さえすれば、」
"I could become young again."＝「また若くなれるのに。」
追加情報：もうご存知かもしれませんが、英語では染色体の末端の部分を "telomere" （テロメア）と呼んでいます。
ご参考になると幸いです。
If I could lightly stretch the ends of my chromosomes, I'd be young again.
"染色体の末端を安く伸ばせれば若返るのになあ"
- If I could lightly stretch the ends of my chromosomes, I'd be young again.
- If only I could slightly stretch out the ends of my chromosomes, I would be young again.
- I would be young again if I could simply lightly stretch out my chromosomes.
アメリカ合衆国 
