Do vampires have to be a certain level to turn a human?

Are you using his ability points? At the second level of vampirism you can choose the turn ability (not at level 2 Vampire Lore, but the minor vampire rank). You can increase his level and get more points by reading the vampire lore books (order them from the phone), and using vampiric abilities like detecting personality, causing hallucinations, dark meditation, etc.

it's been a bit since i've played a vampire but i believe to be able to turn a sim your vampire needs one of the powers. I think if you go in the vampire skill tree for the power's it's one you can choose.

yes just did reserach to reassure myself my advice is correct so your vampire needs to be a minor vampire and will have the option to unlock vampire creation on the vampire power/skill tree.

It's a second tier power that vampires have to choose - you'll be required to have one weakness along with it.

You need the Vampire Creation power. It costs one power point, it's in the second row starting from the bottom, and it's at the right end of the row.

Vampire only has 5 levels: Fledgling, Minor Vampire, Prime Vampire, Master Vampire, and Grandmaster Vampire. If your Sim is a level 5 vampire (Grandmaster), he should be able to get any power as long as he has enough power points and it doesn't conflict with his weaknesses. If he's out of power points, he can earn more by gaining bonus ranks or drink a Draught of Reconfiguration to change the powers selected. The Draught of Reconfiguration is unlocked at Vampiric Lore level 14 and is made at a bar.

@Honeydew
Another way to get more Vampire points is to buy the Vampire Tomes from the bookcase or study Vampirism on the Computer. You should befriend another Vampire and request training as a vampire, that's a great way to get points. The more times you train or use Vampire powers, the more Vampire points you get. Then you need to pick your powers and weaknesses.

Yes, they do. They need to be a Minor Vampire (Level 2) and they need to unlock an ability called Vampire Creation. That will allow a vampire to Embrace humans into vampirism either by force or by offering it to them politely. Having certain number of Childer is a requirement for Vampire Family aspiration.