You're pretty young, so I think you could look to improve in many areas. Your 200m is better than your 400m, but 23 high won't be quite fast enough to go sub 50. Like others said, training like a traditional sprinter with acceleration and top speed work will be beneficial. I also think something 400m guys ignore, at least young ones who aren't blazing fast at 100m, is some cruise interval type work. Think; tempo run, but for a sprinter. So that might just be 200m reps in 40s with a 100m walk or 400m reps in 90 with 1min rest or something similar. But this would only be done once a week in the off season or every other week early season, and maybe sprinkled in elsewhere. Cross training and/or easy jogging might be good on some of your easier days, at least early in the season or in the off season.
Personally I improved my 400m (split) from 53 to 49.9 in one year after upping my mileage from 50mpw to 70mpw, but I was also more consistent with lifting and hard strides / hill sprints. But having a good overall aerobic capacity is good for letting you put in more work when it matters. Which is why some light jogging or cross training may help in the long run, too.
As an example: There was a 200m runner who was a freshman who ran 22.XX mid in the 200m, but typically ran 53-54 in the 400m. He decided to do cross country the next year (he had done it once in high school), and although he'd do less mileage than us and substitute some workouts, he was still doing tempos and mile repeats and stuff, and he went from that 53 400m PR to 48.4 in the open 400m in one year, despite running about the same times in the 200m.
Also, are you lifting? If not, GET IN THE WEIGHT ROOM