Well, my dad died of Hodgkins and I think the fact that he sprayed pesticides on all of his plants for years (he had two very large gardens) may have played a role. Really tough to tell but in his case I think the chemicals played a role.
edit: he sprayed this stuff with zero protection (PPE).
I also think one can look at certain things like everyone having the exact same condition through generations. That might also offer a clue. Hodgkins (I'm not an expert on that cancer), for example, does not appear to have a strong genetic component to it, from what I've heard. Certain other cancers absolutely do. Not everything is the same.
Additional edit: this is from cancer.org related to non-hodgkin's lymphoma:
Some people inherit DNA mutations from a parent that increase their risk for some types of cancer. Having a family history of lymphoma (Hodgkin Lymphoma, Non Hodgkin Lymphoma, CLL) does seem to increase your
risk of lymphoma.
Gene changes related to NHL are usually acquired during life, rather than being inherited. Acquired gene changes can result from exposure to radiation, cancer-causing chemicals, or infections, but often these changes occur for no apparent reason. They seem to happen more often as we age, which might help explain why most lymphomas are seen in older people.
This would seem to back up your point.