lokiez, I can't say yes or no, because we all have different courses to our illnesses. All I can say is what I experienced, and based on my experience, my answer is that my manias were most intense in my 30s. I am 95% sure that my first full blown mania was when I was 15 years old, and I am equally sure that I also had full blown manias at perhaps 21 and 24 years old. They were quite significant, but not even in the ballpark of what I had in my 30s.

I have read that untreated bipolar disorder worsens the course of the illness over years. Again, whether or not that is/will be true for all people with bipolar disorder, I don't know. I will say that I did not receive proper treatment for my bipolar disorder until I was 34 years old during my first of several psych hospitalizations, and it was so severe at that time that my doctors struggled to get my manias under control for quite a while. However, since I turned 40, and I'm in my late 40s now, mania has been less of a problem. I've still had a few, but they were very short-lasting because medication intervention was able to shorten them. Already being on medication surely added in this benefit. Low low stress helps prevent my manias, too.

tecomsin mentioned being on a daily antipsychotic. I'm guessing that is not necessary for everyone, but it seems to have also been necessary for me, since age 34. Honestly, it would seem like a long road for me to travel to get to the point where my psychiatrist stopped my antipsychotic.

Note: Though I likely only had about four full blown manias prior to my early 30s, I did have a very large number of hypomanias before that time that didn't reach full blown. They often lasted long periods of time. They were not bad enough for hospitalizations, but they were destructive for me in varying ways. Prior to my 30s, I had only three severe depressions, plus several short-lasting mild ones. Hypomania and full blown mania (with and without mixed features and/or psychosis) have been far more impactful in my life than pure depressions. I'm more of an "up" person than a "down" one, but I'm not saying "up" is always a good thing.