[PeterisP]

If the probabilities are such that it's feasible that we're the first/most advanced life in the universe, then (given our planets comparably young age) it's exceedingly likely that we're the only life in the observable universe.

It would be plausible for us to be alone, and it would be plausible for us to be one of the less advanced lifeforms among many, but it would be quite surprising if we'd to be the most advanced civilization among many; since many/most of them would have gotten a significant head start.

[greggarious]

Did they get a head start though? All these atoms bouncing around started with the big bang after all :)

One theory I'm fond of is that we are not alone, but life is so rare that the distances between intelligent civilizations are too vast for us to ever observe them (or vice versa).

[PeterisP]

Many, many other planets had conditions suitable (as far as we understand what's suitable) for creating life when our planet didn't exist yet; out of all feasible planets we're younger than average, so others would have had a head start.