I did not get into the fitness field until I was 40. As the others have said before me, being in age close to your clients has advantages.
Having said that, the greatest challenge for novice trainers is to recognize that others of similar age are not in the same physical shape or mental frame as you are. But all of this, you will learn as you study to be a personal trainer. In the end, your interpersonal skills will have as much to do with your success as your training.
It will still be a slow process getting started. So while you are transitioning into the fitness field, don’t quite your day job.
I wish you luck and success.