It's never too late to start journaling. Journaling can make a difference for any age, regardless if you are in your teens, 20s, or 70s. The act of journaling is a personal one, it allows you to better understand yourself, and to help you solve and better understand your inner conflicts, thoughts, feelings, and emotions. These are all things we humans have at all ages of our lives and at any age, which is why it is never too late to start journaling.
In the beginning, it may feel a little bit strange to just sit and write what you are thinking, you may also not really find much to write about. This is expected. It's a normal reaction and feeling, especially if you have never really sat down to write about your thoughts before.
The key is to keep it simple and to keep it consistent. You do not have to write 3 pages each time, and you do not have to do it every single day. If you are not feeling it, don't force yourself to do it. If you have nothing to write about, or only have enough to cover half a page, don't force yourself to write a whole page.
The point of journaling is not how much you can write about something, but what you write about.