Meaning of 腰が曲がる in sentence

皆さんこんにちは,
Just one more quick question. I'm reading a news report about types of food put into 重箱 juubako. In it it says

それに 腰が曲がるまで丈夫 に長く生きることができるようにえびの料理も入れます .

I think it says something similar to...

More over for a strong long life a prawn is also put in.

But what does koshi ga magaru mean in this sentence? The literal meaning seems to be" to bend your back or crooked back"

Is this a metaphor for old age? As in...

Moreover until old age, in order for a long healthy life a prawn is added.

What are your thoughts?

Your interpretation "a metaphor for old age" is correct.

Thank you toritoribesan