By the time the parents of Serena Violano were in their early 30s, they had solid jobs, their own home and two small daughters.

Today, Serena, a 31-year-old law graduate, is still sharing her teenage bedroom with her older sister in their family home in the small town of Mercogliano, near Naples.

Ms. Violano spends her days studying for the exam to qualify as a notary in the hopes of scoring a stable job. The tension over her situation sometimes spills over in arguments with her sister over housework or their shared space. And with her 34-year-old boyfriend subsisting on short-term contracts, Ms. Violano doesn't even dare dream of building the sort of life her parents took for granted.

"For our parents, everything was much easier," she says. "They had the opportunity to start their own life. Instead, we don't have any guarantees for our own future."

Ms. Violano's stunted adulthood and dashed expectations mark a generational divide between younger and older Europeans that is challenging the Continent's dream of broad-based prosperity.