You get to decide who sees you on Match or on the radar, at least in terms of gender and age range.
If you would like to change your search settings (gender, age), you have three options:
Change search settings in Match
You will find the symbol for filter settings at the top right. You can change the gender of your future flirting partners with one click and expand or reduce the age range with the little slider.
Change search settings in the local area / in the radar
If you click on Nearby in the bottom bar of the app, you will also find the icon for the filter settings and proceed as described above.
Change search settings in the profile
In your profile you can find your search settings under “Settings” and you can change them.
You cannot search for people by username.