It is not strange to improve slowly after 25. I find it difficult to improve for myself too. Take care of your stamina, improve your nutrition, take foods which improve you brain functionality and of course devote some time to study. Consider some herb which can clean your systems from inside, because this will also help your brain and mood. Chess is an investment for our mental health as we grow older. Take a look at my forum here http://www.chess.com/forum/view/general/improvement-in-chess-according-to-elo.
I am improving too slow.
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You haven't been playing that long so it's probably not worth worrying about improvement. But to get better, you might want to make sure that you're solid on the fundamentals first.
When you review your games, mainly losses, you may want to ask yourself:
Did I forget to develop all my pieces before attacking?
Did I leave any pieces hanging?
Was my King exposed?
Did I open away from the center?
Did I ignore my opponents moves?
If you have a lot of "Yes" answers in your games, it might be helpful to work on those areas before moving on. In chess, games are much more often lost due to fundamental error than brilliant play by an opponent. Your results should improve just by cutting down the number of needlessly dropped games.
At the same time, working on calculation might also be useful. Getting into the habit of trying to think at least two moves out usually pays off. So it's something like, "If I move here, he does this then I do this and he answers..." Once that becomes common, you want to move the number of moves calculated out as much as possible.
I'm guessing you might be surprised how good your results will be by just being solid on the fundamentals and being able to routinely calc out two or three moves.