Might depend on the terms you have in mind, but current consensus seems to be more like 4-5 years as we speak on https://www.metaculus.com/questions/6728/ai-wins-imo-gold-me...
Solving Millennium problems is a whole different ballgame. It's not known if these problems are solvable within ZFC axioms. (In one case, the Yang-Mills prize, stating the problem mathematically is part of the challenge.) All of the obvious applications of known tricks have been tried and failed. To solve such problems, one probably has to invent new and surprising mathematical definitions, building a framework in which the problem becomes solvable. This is something that LLMs will be crap at; the process of invention is not represented in any training data we have access to.
There are ~1000 MO winners and 1 (one) Millenial problem solver ...
Here's what Andrew Wiles, the only other person to have solved a Millennium-class problem has to say of math competition: "Let me stress that creating new mathematics is a quite different occupation from solving problems in a contest. Why is this? Because you don't know for sure what you are trying to prove or indeed whether it is true."
Nobody argues it's the same, after all MO problems are designed to be solved in ~an hour, but we are talking about mental capabilities.