cut the apron strings

村上春樹のUndergroundを読んでいます。
My mother never watches TV talk shows and had no idea about Aum. When I told her that becoming a renunciate meant we couldn't see each other again, she cries a little. She had no idea. Though she'd thought is strange how my health and appetite had improved. "I suppose it's time for me to cut the apron strings," she said.

"cut the apron strings" も慣用句に違いありません。
・Merriam-Webster's Online Dictionary: to stop providing support: The company has relied on government support, but the government is now threatening to cut the apron strings.
・Urban Dictionary: breaking free from dependency on another person: Once I graduated from college, my mom had to cut the apron strings. she would no longer enable me. Tough love, you know.
・Collins COBUILD Idioms Dictionary: If a person, a country or an organization cuts the apron strings, they become independent. At 21, I was still living the life I'd been living when I was 15. I just had to get away from that, to cut those apron strings. Note: Verbs such as loosen or let go of can be used instead of cut.
元々は母がエプロンの紐を子供に繋いで、家事をしている時でも子供が危険な目に会わない様にしていたことから発生した慣用句で、"the apron strings" は母の子に対する保護・干渉の意味から、上記辞書にもあるように母と子の関係以外にも比喩として使われる様になったようだ。