I agree with everything derby1592 said.

With regard to the possibility of combining age groups to increase sample size, I think you have to let the data guide you. If the outcome for a given pattern or set of patterns is the same for a series of age groups, there's no reason not to combine them. That would allow you more flexibility to break down the data in other ways (such as by breaking out cheaper horses as derby 1592 suggests) without overly shrinking sample size. On the other hand, you may find that you need to separate 6yos and up from 5yos.

The same logic would apply to combining pattern data where the last two races in the pattern are the same.

I'm not really suggesting adding anything new to the sheets themselves, just that by looking at the data you may find more revealing ways to "rack and stack" it (and that I'd love to be able to look at the data myself). I read one book by an author named Cleveland in which, among other things, he bemoans people's tendency to spend a lot more time on data gathering than they do on data analysis. He argues that the such priorities are misguided, particularly since data analysis is usually much cheaper.

My compliments on what you've accomplished so far.