Congratulations on hitting that milestone! And, while there's no guarantee, I'd say there's a good chance of you hitting $1M or more by the time you're 50.
Looking at my own history, I hit $500K in March 2010, just before I turned 40 in April. I hit $1M in February 2015. So for me, about 59 months to get from $500K to $1M. So if you're already at $600K, seems like 7 years would be reasonable, to assume $1M.
Of course, much of it's dependent on stock market returns. Yet, even in my case, there were some rough patches. I was down about 15% in the summer of 2010, but that fall/winter I gained it back and then some. In 2011, I took a 6% hit early in the year, recovered to new highs, and then in the course of a month lost about 14% over the summer. In 2011 I actually lost money, but it was a small amount, only down like 0.12%.
2012-13 were great years, and the first half of 2014 was too, but then the market just fizzed out. I was around $970K by the 6/30/14, and it seemed SOOOO close to $1M. So for that milestone to just sit there, so close yet so far, was aggravating. Now I look back on it and it was like eh, so it took 8 months to get from $970K to $1m, big deal. But at the time, different story.
So, again, congratulations, and keep doing what you're doing! The market is going to rise and fall, and there are going to be drops that seem to push your goal further back. But then, there can be upswings that bring you to that goal quicker than you ever imagined.