Question about equity share with non technical co founder

I was planning to be a solo founder. A friend (not technical, business major) wants to join and handle the business and marketing side.

He’s asking for around 20% equity.

I’ve been building the product solo for 4 months. No launch yet, no revenue, no money invested, just my time and effort.

I’m thinking of offering 20% on a 4-year vesting schedule.

Does that sound fair? Is it too much?