I think that in order to become a successful Mastering Engineer, you need to have participated in all the other processes of creating music before you attempt mastering. I think it’s extremely important to have played at least one musical instrument, or sung, or have sung and played. It’s very important to also learn how to make recordings and learn all the different kinds of techniques that are used to make recordings because Mastering Engineers are mostly people with a huge amount of experience in all those things and they bring the full range of knowledge to the task of mastering.
For example, in my career, I was first a performing musician, and I studied music in college. Then in 1976 with my first full-time audio job, I did studio design and installation work. I learned all the technical processes that are involved in studio systems and interfacing different types of gear.
The third step was actually becoming a Recording Engineer and making a whole bunch of different kinds of recordings of a whole bunch of different kinds of music ranging from Rock to Jazz to Acoustic Americana to Classical. I even did a significant amount of work in audio for ethnomusicology. I didn’t get into mastering until I had about 25 years of experience under my belt.
Finally, I think that mastering work is a great career. There is something new and different every day. There is constantly new music to learn, new equipment and techniques, new delivery formats. Many Mastering Engineers work until very late in life, well into their 70s and even 80s!