My dad wants to become a 50/50 co-founder of my startup. I need advice. I will not promote

I'm 18 and I've been building a software product that I believe has very strong potential. I came up with the idea, designed the product, and built the current version myself. After around 1.5 weeks of work, I already have a functional prototype with great design, and things have progressed much faster than I expected. Now my dad has suggested joining the project as a 50/50 co-founder. My dad is an experienced UI/UX designer and has worked on products for larger companies. He has a lot of professional experience with design, branding, and creating polished user experiences. He has also previously run his own company for many years, although it ultimately didn't become successful. His argument is that while I might be able to build a decent business alone, having someone with significantly more experience involved could greatly increase the chances of turning it into something much bigger. He believes his experience could help avoid mistakes and improve the company's chances long-term. I can see his point. I have some experience building things and marketing. Previously, I created a small project where I managed to build a community, get millions of views online, and gain paying customers in around a week. However, I also realize I might be underestimating how difficult it is to build a truly successful company. The part I'm unsure about is the 50/50 split. From my perspective, I have already created the idea, built the product, and done the initial work. A lot of the core design is already done, so I suggested something closer to an 80/20 split instead which he did not agree with. At the same time, I don't want to undervalue the experience and perspective he could bring, especially when it comes to growing the company beyond just the initial product. What would you do in this situation? Would 50/50 be reasonable, or would you structure it differently? I appreciate any opinions and perspectives. Edit: A lot of people are focusing on the "1.5 weeks" part, so I wanted to clarify. I'm not saying I've built a polished, production-ready product in that time. But with modern AI coding tools, going from an idea to a functional first version of the product can happen much faster than it used to. To put into perspective how much AI has changed my workflow, I checked my usage over the past 1.5 weeks and have used at least 200 million tokens while developing this project. There is still a lot of work left; building the website, hardening security, fixing bugs, adding features, testing, and everything else that comes with turning a prototype into a real business. I know building a successful company involves much more than just creating the initial version. My main question is about how to structure a potential co-founder relationship and equity split fairly at this stage.