That's a pretty broad generalization of a continent with a lot of variation in cultural patterns, economics of housing markets, structure of workforces, etc. Here are some numbers, from 1994, but should give an illustration of the range:

    Share of those at age 25-29 still living in parent's home, %
                      Men   Women
    France            22.5  10.3 
    Germany           28.8  12.7 
    Great Britain     20.8  10.8 
    Spain             64.8  47.6 
    Greece            62.6  32.1 
    Italy             66.0  44.1

Source: http://www.york.ac.uk/inst/spru/research/nordic/gerdem.pdf - it quotes source as EUROSTAT Data by Fernandez-Cordon 1997, itself quoted by Lauterbach and Lüscher 1999, p.430:

Lauterbach, Wolfgang and Kurt Lüscher (1999), ’Wer sind die Spätauszieher? Oder: Herkunftsfamilie, Wohnumfeld und die Gründung eines eigenen Haushalts. Eine empirische Untersuchung über das Alter bei der Haushaltsgründung’, in Zeitschrift für Bevölkerungswissenschaft 24 (4), 425-448.