The quickest ways to gain levels would be to either farm creature kills in the East of the star map where most systems are level 50+ or an easier route will be to level via outposts.
The way to level via outposts will be to find a planet where you can get Iron & Aluminum within your outpost radius. This will allow you to continuously craft Adaptive Frames for easy experience. You can put a bench next to your crafting bench that way you can wait and instantly fill up all your resources.
If you are having trouble finding a spot where you can get both resources in your radius it helps to land exactly where two biomes meet that way you end up with a more dense area.