sell adulthood to me

[frindle2]

Hello. I don't quite understand the underlined sentence in the context below. Would you please tell me what it means?
Does it mean "I" never met an admirable adult?

(The speaker(I) has become friends with Ria's son recently. The speaker and Ria's son are twelve years old.)

"I think it's just so great that you're both fast friends." Ria chirrups as she pours herself a drink. "Treasure that. It's something you can only do when you're young.
I miss that, you know," she smiles widely at us. "Being able to have a new best friend in just a few short hours. It's such a gift."
I've never met a grown-up who has ever been able to really sell adulthood to me.

Source: Show Us Who You Are by Elle McNicoll

 

[Skrej]

Imagine that adulthood is a product you can buy. The speaker hasn't met anyone who would be able to convince her to buy such a product.

She's not convinced that being an adult is really all that great. If it were a product, she'd be unlikely to buy it. No adult has every been able to convince her that being an adult is so great.