Absolutely. But that's not, as I understand it, why it's called a spectrum. It's called a spectrum because it covers conditions as different as Asperger syndrome (which often isn't diagnosed until adulthood, and may never get diagnosed at all) and childhood disintegrative disorder, where the onset of symptoms is so sudden and dramatic that the child themselves may notice and ask what is happening to them.

Being "nerdy, introverted and eccentric" doesn't necessarily mean you are on the spectrum. It may do: you may have an ASD, diagnosed or undiagnosed. But it may just mean you are nerdy, introverted or eccentric.