You are never too old, in years, to start a Doctoral program or to otherwise extend your education. However, you need to do a couple of things while you "wait".
Most important is that you don't lose your edge. If you are working in the field of study you should probably be fine and your experience may help. In fact, it may give you some ideas about unsolved issues in the field that might lead to research and a dissertation. But you will also need to try to keep current through readings. You don't say which field you plan to enter, but some move faster than others. New possibilities for research open up as well.
The second thing is that you will need to be prepared to answer questions about the gap in an intelligent and positive way. Getting experience in field is a pretty good answer. Recovering from burn out is not so fine.
However, as you age, you may take on additional responsibilities that you don't now have: family, kids, mortgage, ... Seek life balance of course, but as your responsibilities change, so may your goals. You will also need to deal, increasingly, with the needs of others. But nothing is an absolute block.
Remember that you will age no matter what you do. It is better to spend your life doing something you love than otherwise, even if it takes a while to realize the dream.