Is this legal in a 'roommate wanted' ad?

If I’m not mistaken, a roommate situation doesn’t have the same legalities as an apartment rental or house sale. For example, you can say you want a female roommate. You couldn’t say you want to sell the house to females only.

Seems legal to me. You can discriminate as much as you want for a roommate or even renting out your entire property if you are just renting out one or two properties. Maybe there is a few states that say differently, but that’s the norm.

Edit: Fair housing tends to kick in for 4 or more units.

I agree with the above. You’re not selling something you own so the Fair Housing Practice wouldn’t apply.
The religion-specific thing is kind of odd…but not illegal.

My mom was a high ranking official with a state housing agency and I recall her saying what @JLeslie said, about the 4 units, and also the critieria is different if the property is owner occupied, at least in NY state, and so a roommate situation is “owner occupied.”

Edited: Forbes Advisor:

https://www.forbes.com/advisor/mortgages/fair-housing-act/#:~:text=When%20advertising%20the%20sale%20or%20rental%20availability%20of,housing%2C%20which%20is%20otherwise%20exempt%20from%20the%20FHA.

I grew up in Utah, which has a high population of Mormons. The last 8 or so years we lived in Park City, Utah. Park City was not particularly friendly toward the “no drinking, no smoking,” requirements of the Mormon religion, so for a while they had a law that if you were advertising for a roommate, you could not specify no smoking, no drinking or no drugs.

It seemed to me that that law infringed on the disability laws, which would include people with medical conditions such as being on oxygen. Obviously if you are on oxygen, you cannot be in a home where there is a smoker present..

This was years ago. I checked recently and there no longer appears to be any restriction on roommate housing.

Seems legit, to me.