The advantage in France is that friend cohorts are likely moving to Paris roughly at the same time. But moving further out into the suburbs or returning to the

The advantage in France is that friend cohorts are likely moving to Paris roughly at the same time. But moving further out into the suburbs or returning to the province / a city nearer their hometowns to start a family is comparable to the US - just my guesstimate. And as someone else pointed, friends living on the RER or opposite side of Paris might as well live in another city, unless meeting up somewhere halfway instead of at someone's place, but that can quickly get expensive.