He doesn't seem very mature, however hard he is trying.

There were/are a lot of non-negligible issues when you've 'only' been together for 6 months. This should be an idyllic period... not one fraught with doubts and his ill-placed 'jokes' and/or frustration when he doesn't get his own way.

Just the fact that you are asking this question and having doubts show you are not really (emotionally) satisfied. I would not dismiss these doubts.

I would be very cautious proceeding forward with that guy.