>>235
Mr./Ms.Sling's question, the answer is always the difficult one. 　　LOL　^ 。^；

"ヒダヒダ" is not in the loan word and onomatopoeic though this ia writen by the katakana.
ヒダヒダ＝ヒダ×２
ヒダ⇒ひだ＝襞＝Plait/Fold
Crease such as skirts
Thing that seems to be folded thinly. ←Have you seen the inside of cow's stomach?

But in your case "Example: 若いヒダヒダ",
It will mean a part of the body that the man doesn't have. ⇒"Inner lip（小○唇）"
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Though neither Hidai nor Hidahida are related immediately, indirectly.................
彼女の下腹はヒダイ（肥大)化してヒダヒダに為っていた。
She had the abdomen in Hidahida for the expanding fat