How can you tell the difference between a simple delay that will resolve itself and one that won't? You can't know for certain, so the best thing you can do is to get an evaluation. Even then, the evaluator may be unable to predict whether your child will "grow out of it" if your child has subtle delays and is quite young. In such a case, the evaluator will probably recommend therapy to address mild delays or to monitor development.
Another aspect to consider is how many age-appropriate tasks are too hard for your child within a particular skill area. If your five-year-old can string beads, assemble a jigsaw puzzle, build a fort out of Legos, and button her shirt, but can't use scissors, does she truly have a fine motor delay? Also, a child who is delayed in one area is quite likely to have other delays as well. At the same time it's quite common for a child who is delayed in one area to be ahead of the game in another area. It can all be very confusing, and for a parent, upsetting. With so many variables, it's essential to get professional help to identify and sort out your child's strengths and weaknesses, and to provide appropriate interventions.
We'll give you a few developmental benchmarks here (based loosely on a combination of developmental scales), but keep in mind that age expectations vary between scales, evaluation is subjective, and most developmental delays are not an irreversible, major catastrophe.