is there any correlation between time of first solo and subsequent quality as a pilot?
I suspect it's akin to how long it took to learn to ride a bicycle to how good a cyclist you are after a few years. (i.e. zero correlation)
Not that going solo soon is not an achievement in itself - it's just that all (well most!) of us get there in the end anyway. Going solo at 60 hours is not unheard of (you would have to admire the persistence of someone like that)