That's great James. There shouldn't be anything to hold you back from racing. Just jump in at the deep end... a 2/3s road race or similar MTB race. British Cycling www.britishcycling.org.uk
will help you find a race.
With regards to testing, there really isn't any substitute for an appropriate (perhaps an exercise and physiology) lab where procedures are routinely carried out and quality control procedures are in place. Fortunately I have access to equipment that measures oxygen (and so VO2 max) directly so haven't had to use the polar to estimate this. You can also get a list of labs from BC or www.BASES.org.uk
and don't forget the importance of lactate threshold.
Although I am unable to assess the quality of your gym instructors, it was only 6 months ago that the BBC reported how badly qualified gym instructors are in the UK. Many courses (and I appreciate not all) are less than one week in length/one weekend and after going on the course instructors are expected to perform a range of functions from cleaning toilets to developing programs that reduce blood pressure in 80 year old women. Instructors in other countries are required to take much longer and more formal qualifications before instructing people in exercise. I wouldn't even trust my doctor to use calipers on me! I would check the qualifications of your gym instructors and also check what data you are being compared to when you are given predicted values; norm data needs to come from a population that represents you, not the whole population or just men or even just all men of your age. A good instructor will be able to inform you of the limitations of the test being performed.
Given that you find the gym so easy now it might be good for you to progress your training or make it more specific with more time spent on the road or in the woods. This will help you get even fiter and as VO2 suggests... a coach might help.
With regards BMI, it may be correct that Lance has a BMI of 22-23. In reality, BMI has little use other than telling you whether or not you are underweight, normal or overweight compared to the normal population. With this information you can decide whether you are at risk of respirtory (underweight) or cardiovascular illness (overweight). People from athletic populations are normaly outside this e.g. body builders often have massive BMI's but are at no risk of CHD unless they take steroids and the like. Endurance cyclists tend to have very low BMI's simply because they carry little fat or muscle, again they are at low risk of CHD or respiratory illness.
The reason that I state that your low body fat may be a problem is that men and women have non essential body fat and essential body fat. For men it is often quoted that 3% body fat is essential and when body fat drops below this many processes in the body can start to go pear shaped, fat is also used to store some vitamins, insulation, crash protection, the production of cell membranes, hormones, etc. these factors can effect health and performance when fat gets too low. I would advise you to monitor your body fat closely if it really is that low.
Back to the original question, just go racing... it can help to choose races unaffected by tactics when you start (particularly when you are fit) as this allows you to have success faster.
For coaches contact RicStern (a moderator of this forum), BC Coaching and Education or www.abcc.freeserve.co.uk.
Looking forward to seeing you on the start line.