Most people who call themselves Rajputs are Jatts. Jatt is a kaum. Jatts can be Rajputs only if their parents or grand parents were rulers of some land. Again it was a temporary title. But some people like to feed their ego and carried/carrying on with such titles even generations after generations.
And regarding Sikh, it means learner/seeker the word is derived from Sanskrith language.
Moreover, nobody is a born Sikh. One becomes a Sikh by following the teachings of a Guru. So there could be different type of Sikhs in this world since they could be following different teachings.
Now think about some Christians, Muslims, Budhists, and Jains. Are they following the teachings of their Gurus? If yes then they are Sikhs of their Gurus. So Sikhs have been around on this planet for a long time. So it is very hard to decide who became the first Sikh.