If I read this correctly, this happened earlier this year - and nothing else has happened since then. This is also not uncommon for young boys to experiment.
I think that the fact he came to you and confessed so much longer after the fact, means that he is still troubled by either the experience or (perhaps your reaction). Either way, I think it would be appropriate to congratulate him for telling you and make sure that nothing else is still bothering him.
I agree, i think its very important to have good communication with him.
He feels comfortable enough to tell you.
this is perfictly normal behaviour simply observe from a distance and be their to talk to your son when he needs it, at times this will not be easy as everyone should be well aware how embaasing such conversations can be for children that are getting close to puberty. a fairly common occurence is a genitic trait known as precocious puberty where a child starts to go through the early signs of puberty a few years early between 7 and 9 for males and 6 and 8 for females. however this is nothing to worry about as it is natural and has some benifites. such benifites are that while they remain in puberty for an extended amount of time the sudden mood swings and other effects of hormone increases are reduced somewhat.
however It is more likely that your son is just curious and is starting to experement like most boy do around that age. the best thing to do is simply observe and explain thing to your son as needed, don't push him but set boundaries and talk to him about what he needs to know when he needs to know it.