I am 51 yo, started cycling 2 months ago. I do about 80 km per week (in weekends). Currently my average speed over large distances (max distance I've done so far is 90 km) is around 22 km/h. On flat surface, 600 m distance I currently reach on average 33 km/h, but after about 300 m I lose speed. Two months ago I was doing about 30 km/h. My peak speed is about 41 km/h, for very short distances. Do I have any chance to reach an average speed of 40 km/h over 600 m within one year?
Without knowing any more detail, the goal is probably achievable but you won't do it by riding harder, you need to train smart(er).
Given you just started cycling, if you have not had any coaching, you are probably close to fit enough to do it with improved techniques. You should therefore focus on training, not riding. If you train to ride, rather than ride to train, you will become a stronger rider. How much training vs riding is up to you - no point spending all you time training, especially if you don't enjoy it as much.
I suggest getting involved with a local cycle group, and maybe seek advice from a cycling coach. If you don't want to use a coach, look around the internet for training ideas and plans. Be careful not to overdo it.
Perceptively, its always as hard to ride. So one of the best tools is accurate record keeping to show your improvements over time.
Personally I use Strava on every ride to record my route and times. This lets me compare my times on marked segments for improvement. Strava has an app that works on most fancy-phones. You can also get a chrome plugin called Elevate that shows cumulative graphs for distance/elevation over the year or for the last N days.
Unless you've gone full-MAMIL and bought all the kit, there's a good chance you're still working out what equipment works for you. Keep revising, and don't hesitate to try different ideas for gear.
So how much improvement should you expect? More than you'd get for doing nothing and sitting on the couch all day - and that's all that matters.