How much can I expect to improve in 1 year? 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.