My immediate answer is, "HECK NO!" He has literally saved the universe once and the Earth more than a few times. However, maybe, just maybe he is.

Let's take a look at his chronology, shall we... Quasar first appeared in Captain America #217 which has a publication date of January, 1978, 22 years ago. This takes place chronologically after Marvel Boy destroyed himself with the Quantum-Bands in Fantastic Four #165 with a publication date of December, 1975. With the 10-Year Rule in effect, the time available to Wendell to participate in all of his adventures is somewhat compressed. If we go with proportions (I do realize that some of the early Marvel stories happened in real time, but proportions simplify the math, and there's not a lot of agreement on just how much real time elapsed in the first couple of years), the Fantastic Four has been around for 39 years. These years get crammed down into 10. 39 years is to 10 years as 22 years is to 5.6410256410256410256410256410256 years, or approximately 5 and ˝ years. This would be the number of years since Wendell's first appearance.

However, the plot thickens. According to Quasar #2, Wendell spent "over four years" in suspended animation asleep (Wendell thinks to himself that it had been over 4 years since he had done any type of exercise). These are absolute years, not Marvel time-compressed years, otherwise they'd turn into about 4 seconds. This does not mesh with his mentioning a 6-year round trip in Quasar #3. This implies a travel time of 3 years there with an identical 3-year travel time back. The only explanation that seems to make sense is that due to planetary orbits the distance there differs from the distance back. This gives us Wendell's "over four years" to not exercise with 2 years for the return journey. So, subtracting 4 years from the available 5.6 years (from above), leaves 1.6 years for him to have experienced all of his adventures from Captain America #217 until the present day. This does not include his actually acquiring the Quantum-Bands and his initial S.H.E.I.L.D. Super-Agent training detailed in Quasar #1. However, it does include his time as Head of Security for Project Pegasus, the adventures chronicled in Quasar, Avengers, Starmasters, etc. Also, Wendell has only aged 1.6 years since first appearing due to the over 4 years he spent in suspended animation. Thus, we can compute Wendell's present age from what know about him. He spent 2 years at the University of Wisconsin - Oshkosh and 4 years completing S.H.E.I.L.D.'s Agent Training Program. Assuming an age of 18 when entering college, Wendell is presently approximately 25 years old (physically). However, computing his age using is birth year would make him 29 years old, since it includes the 4 years he spent in suspended animation not physically aging. Being 25 explains several of the "kid" remarks when interacting with other heroes (most notably during the Infinity Gauntlet) and puts him much closer in age to Justice (Vance Astro) and Firestar (Angelica Jones).

So, after looking over all of the evidence, I would have to say that in experience, Quasar is not a rookie. However, his age belies his experience and makes others think of him in that respect.