More speed, sir

I've been swimming now for about 4 months after taking nearly 20 years' hiatus. Needless to say, I'm not really not trying for any speed records but I'm frustrated that I'm not getting any faster. Ironically enough, I'm usually the fastest swimmer in the pool, even compared to other 20 somethings. Then again, there really isn't much competition at my 24hr fitness. I've been told by others that my form looks pretty good. I can swim 25m in about 15 easy strokes. But I can't seem to get my arms to move any faster in the water. If I try to increase my arm speed, I end up compromising my extension, using more energy and going about the same overall speed. Since I've been focused on distance, I've been using a 2-beat kick. I'd like to employ a 6-beat kick, but somehow can't get the timing down. When I try for a 6-beat, I usually end up fluttering around like a wounded minnow. I swim about 5 times a week, mixing up distance, speed drills and kick drills. I'm 33 years old, decent cardio, height 5'7". So I'm open for opinions. Should I focus on increasing arm speed? Work on a 6-beat kick? Increase strength? All of the above? Thanks