Would you be willing to start your career with old, proprietary tech?

Debating on whether or not to accept a job offer for my first ever job out of college.

Company told me that they had 2 projects that they were working on: maintaining a 10+ year old legacy project, and a newer project that would be built from the ground up and was still in the process of forming a team.

Initially I was to be assigned to the newer project. I asked what stack it would be using, and they showed me a chart for it, there were a lot of new and familiar names both open source and proprietary. I was sold on the idea that we were gonna learn and apply all these tech and make something original on our own.

However, some time after I was then told that Id be working on the legacy project instead as that was their priority. I asked for the tech stack again, and was just told that it was going to be Java 8, SQL, and the rest were proprietary software (which were not named). I asked what the day to day would be like, its gonna be 3-6 months of training, then afterwards its just gonna be fixing bugs that clients submit.

It was a bit of a downer tbh cuz I already set my sights on the newer project. Pay is decent but not competitive. Plus its 5 days onsite. I was willing to overlook that and focus on the growth, but with the change in project assignment im sort of worried that I may not be doing myself any favors with dated/proprietary tech. Plus already did bug-fixing for the majority of my internship, and while not a bad experience, I feel it did little for my growth (anyone else feel this way with debugging?). So far I'm on the fence, but I think I'll ask anyway if I can start on the newer project and pass on the offer and look elsewhere if not. Is this a good idea? Or am I just jaded after changing projects and does the legacy project sound like a good place for growth still? Ive been told that if ever, I can switch projects after a while, which I think would take 9 months to a year (taking training into consideration).