When should i set a wedding date?

You would likely need to set a date more than 9 months out. Venues and other vendors book up 1 to 2 years in advance. If you want to get married in September of 2021, I would start looking at venues in the beginning to middle of 2020.

I'm not sure what you mean at the end?
If you want a September 21 wedding you'd start planning and setting a date roughly a year in advanced for it.
You can announce an engagement anytime, that's up to you guys if you want to wait until September of this year that'd probably be good timing. You just can't a lot of vendors or venues anything this far in advanced.

September/October are the most popular wedding months... in June of 2018, they told me that September and October of 2019 were already fully booked at our venue (luckily we wanted June 2019 anyway which still had some availability, but just goes to show how popular September and October are). I would start looking at venues maybe around 18 months before your wedding if you want a September wedding, though it depends on the type of venue. My friends getting married this September booked their venue I think 15 months in advance. But my friend who got married last October and just had her wedding in the private room of a restaurant, booked it I think like 3 months in advance, but obviously that's less of an in-demand wedding spot.

And this is unsolicited advice but, as someone who also got engaged while still in college, I'd recommend maybe giving yourself another year before the wedding. I got engaged in December 2017, graduated May 2018, got married June 2019. I didn't even start planning until May 2018 after I graduated, which was really good to not have to worry about the wedding while still in college. If you give yourself an extra year then you don't even have to worry about any of this until graduation which I would advise. That's just my experience though!

I got engaged my junior year of college (2015). We didn't even start considering dates then because I wanted to make sure I'd get a job when I graduated, luckily I did (2016) and we were able to come up with a reasonable budget and set our date for July 2018. So I recommend just enjoying being engaged for a while and don't worry about a date just yet. If you want September 2021, you'd want to start looking for a venue in spring/summer 2020