It's hard to imagine gradually cutting back simply due to waning interest. I've been chasing for a decade, and a good tornado day still brings a high that practically nothing else can. It's no secret that this is a highly-addictive hobby for a large percentage of those involved.
You know how scientific studies have found that when people plan a vacation, it's often the anticipation/build-up that brings them more happiness than the vacation itself? In other words, when they finally get to their destination, it rarely lives up to their lofty expectations. So many things in life that society tells us to value and work toward have that in common - they may be good in the moment, even great, but they don't quite live up to the hype. But chasing does, for me. The reality of standing in front of Rozel or Bowdle is actually everything you imagine it to be all through the off-season, if not more. It's essentially like bringing your dreams into the real world for a 10- or 20-minute period. Things like that are very hard to find, and equally hard to ignore once you do.
Unfortunately, some of the same things that make it so addictive and fulfilling - the adventure, the risk, the unpredictability, the escape from the "real world" and structure and artificial schedules - are precisely what cause friction with many other compartments of our lives. This is why Dan's advice is so prescient: if you're lucky enough to have discovered your passion for storms at a young age, take full advantage while the consequences for doing so are minimal. The older you get, the more you have to consciously maintain a certain lifestyle and set of priorities (that are well outside the mainstream) to keep chasing the same way. In general, this means more sacrifices for the same amount of chasing, as time passes.
After all that pontificating, I don't know if I have an answer to the thread's question. I see some chasers in their 30s and 40s who gradually scale back and seem perfectly happy going out on the 2 or 3 high-end days within a state's drive (or doing an annual week chasecation, if living elsewhere), and in many ways, I hope I can get there without too much consternation. I do know that other hobbies, even those that bring you closer to nature like hiking and skiing and landscape/wildlife photography, can be rewarding - but in a different, subtler way. If I'm being honest, I can't say that any of those things evoke anywhere near the same passion in me, and I wonder if experiencing the absolute thrill of chasing has made them "look bad" by comparison! These are the issues that probably 90% or more of serious chasers in their teens/20s have to grapple with as they age.