From my understanding, the application of the word "gulag" to a prison is to indicate there is strenuous forced labor in harsh conditions in a distant location free from public scrutiny. The implication is that people die from being overworked or due to exposure and the government is able to cover up these deaths because of the remoteness of these facilities. Likely, this implication is meant to harken back to the labor camps of Nazi Germany.
This is irrespective of whether or not Soviet labor camps should be characterized this way or whether US prisons are inherently more humane. If anything, I highly advocate for referring to US prisons by a more pejorative name to indicate their cruel nature. I would use the term "gulag", but I think what makes US prisons cruel is different from a labor camp and deserves a different name.
I guess the question is: what problem are you trying to solve by instituting age limits and term limits?
If the issue is the advantage of incumbency and having entrenched politicians with large campaign funding operations behind them, then maybe a better way of solving this would be campaign finance reform that prevents private dollar donations from non-individuals and heavy restrictions on how much an individual can contribute.
All that term limits and age limits in Congress would achieve is setting an artificial barrier for those who do the job well while setting up a new group of people to benefit from the legislature's dysfunction.