Sam,
Welcome to this site. I'm sorry you need to be here, but hopefully you'll find the information and support you need.
I was diagnosed with tongue SCC (Stage two) 15 years ago at age 39. At that time, my husband and I had been trying for quite awhile to have children, but based on what I heard about the impact of surgery and radiation, I decided it was best to try to put our plans on hold. I should add that we had tried for so long -- unsuccessfully -- that I was on the verge of pursuing either IVF or adoption as possible alternatives, but also put those off as well due to the cancer treatment. Frankly, I don't know how I could have dealt with pregnancy while going through radiation; as you will see from many of the posts on this site, radiation to the head/neck is extremely debilitating even for people who otherwise seem very healthy at the outset.
I don't think your oncologist is being overly conservative -- I think the word is realistic.
Cathy