In case this hasn't been clear: the 'rank' just has to do with how many posts you have. It will change with time as you post more.
As for whether it matters or not... The content of your posts is what really matters, although additional deference tends to be given to those with high post counts. It's an imperfect proxy for the expert-iness of someone. That is, the more posts they have, the more likely they are both to have consumed and to contribute valuable content. Everyone knows newbies will have some rough edges and blind spots, though, so in that regard a low post count can actually be a benefit.
Few (not none but few) will be the criticisms leveled at newbies; more will be the criticisms leveled at longer-standing members; greater will be the tolerance for unsavory character flaws exhibited by veteran members.