Meh, if you can't do the job now, there is no point applying now, i doubt anyone would bother waiting with your app few months, it would probably get lost somewhere there in the mean time, just apply when you can.
Can you be considered active without actually having a high average post rate?
sure, we do not base activity simply from post count/rate. that being said, if you are posting once a month and not showing your presence anywhere, it's probably safe to assume that you're not very active. there are several other factors as well, but what's most important is that you feel that you are active enough to hold the position.