Know this sounds like classic BS but I used to be able to kick 55-60 and 50+ pretty reliably.

• You gotta practice it. Every opportunity at training I was sending it long, and when everyone was taking potshots at goal after training, I was behind the goals sending them back as far as a can.
• Don't skip leg day (if or when you start going to the gym). Particularly hamstrings
• Don't stab at it. Sounds stupid and basic but the amount of people that don't follow through with their kicks is astounding. Again you just gotta practice it

FYI though, I'm 190cm+ tall so having long legs and levers to swing through helped significantly I think. I was never remotely flexible though for what it's worth