1. Yes. We're always born autistic. One can't become autistic later in life, though appearance can change so that one looks or functions as "more autistic" at any age in response to various things.
2. No, not always. We're not all savants, and certainly not all savants in those two areas. I'm bad at drawing, decent at math.
3. Yes, easily. Lots of autistics go until adulthood without diagnosis, or never get diagnosed. Diagnosis was (and is still, though to a slightly lesser extent) based on stereotypes about autistics, and if one didn't fit the diagnostician's stereotypes, they might not get dx'ed autistic, and instead get dx'ed something with something else, for example schizophrenia. It's also possible for an autistic to go through life without any diagnosis, just knowing that they're really odd, and not knowing why.
4. Okay, how to tell whether one is autistic without getting a professional diagnosis. This can quickly get long. Strong sense of relation with other autistics is a good way, as is instinctive nonverbal communication with other autistics in real life, though we can't communicate at ease with every autistic in existence, it's sort of like there are dialects of our nonverbal communication system that aren't always mutually intelligible. Sensory hyper- or hypo-sensitivity, plus certain types of sensory processing that are more common in autistics (processing parts of objects instead of the whole, seeing things as colored shapes and not objects at first, auditory processing disorders, and Irlen syndrome are all more common in us.) If one has had strong interests in particular subject areas throughout their lives, that's a good indicator, as is general social awkwardness when around non-autistics, and inability to learn non-autistic social rules. Language oddities are too, for example: echolalia, delayed speech, difficulty understanding figurative language. There's probably even more that I'm forgetting. Oh, there's also stimming. (Stuff like rocking, flapping one's hands, listening to the same song on loop, flicking one's fingers, staring at fractals.)
5. A lot of people split autistics into high functioning, low functioning, and Asperger's groups, but said functioning labels aren't actually useful. Functioning level depends a lot on environment, and the viewpoint of the observer, and doesn't necessarily say that much about the actual autistic person.
6. I don't know what you mean by normally. If you mean speak, live "independently", drive a car, keep a job, and have 2.5 kids, that depends. I don't see this as something to strive for. Basically I support the idea of autistics living in the way that is most effective. If typing instead of speech is, then I'd much rather type. A lot of autistics don't live "independently" in the way most autistics think of it, though many also do. Some live in their own homes or apartments but have support staff come in. Many of us can't drive because of perceptual stuff. Some of us (like me) don't want kids and aren't particularly interested in marrying. We can have jobs, and be very successful at them in some cases, but the working environment really isn't designed to be compatible with autistics, and the hiring process is skewed against us.
7. Not necessarily with all people, but I think gender hardly ever has anything to do with it. We tend to be better at communicating with other autistics than non-autistics, and may have no problems whatsoever communicating with some autistics.
8. I'm not quite sure what you mean by genius other than that specific range on IQ test results. If that's what you mean, no. Autistics are found in all ranges of IQ test results, though most of such tests aren't great for measuring the intelligence of autistics. Raven's Progressive Matrices *is* good, and shows that we tend to be a lot more intelligent than people think we are. (Outsiders seem to be split on whether we're all "geniuses" or all "retarded.") On other IQ tests, we tend to have a lot of scatter on different subsections, and the average can be pretty meaningless.
9. No. Not yet, hopefully never. I'm a functional autistic, not a defective neurotypical. I don't need to be fixed. I'm neither better nor worse than non-autistics.