As one of the Perl 6 developers, my suggestion would be to wait a couple of months. There have been some very exciting developments with the new JVM backend for Rakudo Perl 6, like new work on threads and very significant speedups on longer processes. But it's not quite yet ready for prime time -- there are definitely still some rough edges. The rate of progress on it has been phenomenal -- it essentially didn't exist at the end of March, and passes 99% of the Rakudo spec tests today. I will be very surprised if the current issues with it still exist in October.

That said, there really haven't been too many major changes to the language itself (as opposed to the implementation) in the last couple of years. I have several modules I wrote 3+ years ago, and keeping them up to date with the language has only required trivial changes in that time. You could certainly start learning the language today using the Parrot implementation with the knowledge that something better will be along very shortly.