Being the client of a prostitute under 18 is a criminal offence, even if you claim to be unaware of the prostitute's age.
On-street prostitution is very widespread and many sex workers on the streets are from eastern Europe and West Africa, also many small brothels exist employing only one or two prostitutes.
Most of the women that you can see along the roads are healthy and quite young (20-25).
They are not at all drug addicts, as prostitution abolitionists (aka the religious nutcases) might want to make you think. And there is lots of money involved in Italy’s sex trade.
Trade happends in Italy's seedy streets where young women offer quick relief for a 20 to 30 euros. Many Italian men from North Italy conduct frequent weekend sex vacations by crossing the borders to Austria and Switzerland where they are able to enjoy cheap legal sex in well equipped brothels instead of dealing with Italian street prostitutes.