By all means go on a diving course (any time underwater is useful experience), but aware of the following:
a) A lot of the stuff you learn is not that useful for cave diving and you will have to even "unlearn" some things.
b) The courses available seem to always lie on two extremes. Either "get you diving as fast as possible" or "get you diving as slow as possible". Neither is very satisfactory.
c) A very considerable problem about the kind of pedagogics used to teach open water diving to beginners is that it revolves almost entirely around facts and fixed routines. This is not the kind of mentality you need for cave diving. To be a good and safe cave diver you need much greater analytical skills. You need to be able to assess risks yourself and you need to stay calm in an emergency and think before you act, not launch into some pre-prepared scenario. Most importantly of all you need to learn about yourself, how you react to stress, what your motivations are and so on.
Just to illustrate the point, I remember having a whole session in the open water diving course I went on concerning "how to get into the water". Well, this seemed pretty obvious to me to begin with. However, in cave diving the answer to this is amost always "crawl/stagger in a most ungainly fashion", except for the occasional excitement such as abseiling directly into a sump. So I wouldn't say that I benefited very much from that particular educational experience.
One caveat is of course that my experience dates from 15 years ago. It might well be that case that with the advent of much more technical diving, that there are new and better educational forms available.
If you are serious about cave diving, I recommend that you take contact with the Cave Diving Group sooner rather than later. I also recommend that you read through one or two cave diving manuals BEFORE learning to dive. That way you are in much better position to make sensible judgements for yourself about what you are being taught. However, don't try to openly challenge conventional diving wisdon - that's a sure way to end up as a pariah. "When in Rome do as the Romans do".
Mark