海老
Old People of the Sea
... 和語の「えび」は、元々は葡萄のこと、あるいはその色のことを指す言葉であった。葡萄の色に似ていることから蝦・海老のことを「えび」と呼ぶようになった。現在でも「葡萄色」と書いて「えびいろ」とも読む。「海老」の字は、長い触角（ひげ）と曲がった腰を老人に見立てたものである。
The Japanese word, ebi, originally referred to grapes (and their colour). Shrimps came to be called ebi because of how they resembled the colour of grapes. Even now, dark, grape-like purplish-red colours are still read as "the colour of grapes (ebi)".
As for the use of the kanji characters 海 ('sea') and 老 ('old people'): shrimps are likened to old people because of their long beards (feelers) and curved backs.
Of prawns and their likeness to grapes and the elderly.