That all depends on the plant, for the most part. I think the general concensus is that if you grow a plant in appropriate conditions for about five years, you will have a mature plant which produces "full size" pitchers.
However, some species can reach maturity in as few as two years, some can take longer than five.
Another factor to take into consideration is whether or not the plant came from a cutting, Tissue Culture, or seed.
Cuttings are just segments of an already mature plant. They, depending on your point of view, are already as mature as the plant from which they were cut. Cuttings do not necessarily need to "grow up." If planted in the appropriate environment, these cuttings grow up as mature plants. The size of the pitchers and such depends on the development of the root system and feeding -I guess that's just to say "giving the plant what it wants" is what is important.
Plants grown from seed are essentially starting with a clean slate, and they take the longest amount of time to mature -as opposed to cuttings of the same species.
I have heard that, in general, Tissus Cultured plants reach maturity faster than seed-grown plants. However they still need time to mature and "grow up" just like seed plants.
As far as lower "rosette" pitchers, intermediate "whatever" pithcers, and upper "climbing" pitchers are concerned:
A plat starts out producing lower pitchers in a rosette. After a while (with most, but not all Nepenthes) the plant will start to form a stem. Intermediate pitchers grow on this stem. These intermediate pitchers share characteristics with lower and upper pitchers.
If you keep the plant happy for a couple of years or so, it will start to "climb" that is, the stem will really take off and vine all over the place -once again, not all Nepenthes do this. The pitchers on this vine are the upper pitchers or "climbing" pitchers. These are the slender pitchers with the loopy tendrils that you see in pics.
To make a long story short, it can take a couple seasons, or years, for your plant to produce climbing pitchers.
I am not ceratin if the plant has to be considered "mature" in order for it to produce those pitchers... maybe maturity and climbing pitchers go hand-in-hand... I think that may depend partly on your opinion.
-Trevor