I think the first and foremost limitation is technique. This is easy to verify since most of us have seen the aged, the out of shaped and women serving bombs.
So forget all those "variables". Focus on technique. However, this area alone is quite murky and tricky enough in that you can't clearly see the line between technique and your potential. I mean, for example, I think I have a relatively sound technique but the serve is still slow. I dunno it's my technique or my strength.