How long ago the Jezero crater was formed on Mars? And is it a meteorite impact crater?
The German Wikipedia Article states that the Jezero crater lake (note: this only referres to the lake, not the crater itself!) is estimated to have existed around 4 billion years ago.
In the English version, it is said that
the delta may have required a period of $10^6–10^7$ years to form
This means that the crater must have existed for at least around 4.001 billion to 4.01 billion years.
Regarding the formation of Jezero crater, in the German Wikipedia Article, it is said that it was created through the impact of a meteorite. Apparently, this is quite sure to say as the meteorite hurled layered silicates or phyllosilicates onto the surrounding areas; those can still be found today.
Note: It is probably not possible to determine the age of the crater exactly (maybe Perserverance will help understanding this better) and I could not find any direct age, but I hope this somewhat helps.
Jezero crater is roughly 50 km across, and it is emplaced within the wall of Isidis crater ("basin"). Isidis itself has seen a lot of erosion, but it has been dated by lots of different people through the use of superposed crater counts (craters on top of it, with the number-age relationship tied to the Moon) to somewhere around 3.85–4.05 billion years old, including by me (Robbins et al. 2013). Jezero cannot be older than Isidis, so it is capped at 3.85–4.05 billion years.
Jezero must have been formed when there was liquid water on the surface of Mars in enough quantity to form a delta deposit. That would mean that it should have formed by the Late Hesperian chronostratigraphic epoch, which dates, in various chronologies, to about 3.00–3.65 billion years ago. So, Jezero formed at least 3.00* billion years ago, but no later than 4.05* billion years ago.
Beyond that, no one that I know of has done superposed crater counts on Jezero's rim to try to model its age. Jezero is highly degraded, and it has only one larger crater emplaced on its remaining rim, making any such crater counts highly suspect. This is why the work I linked to above, I only tried to date craters >150 km, and even that is somewhat suspect. Jezero certainly has deposits in the floor (such as the delta), so any dating of the floor from craters would only be a minimum age because it can't be younger than its floor deposits. Therefore, even if someone does try to do superposed crater counts to get an age for the crater, I don't think they will be successful in getting a very good one. For example, this paper found that the age of the floor deposits is 2.6±0.5 billion years, so again Jezero is at least 2.6 billion years old, but that's a minimum, and the floor deposits must be younger than the crater.
*The Mars crater chonology has an uncertainty of a factor of 2-ish, so even though there are two decimal points on my numbers, treat that with a grain of salt.
And yes, an impactor formed the crater, either an asteroid or a comet.