How much should I save up to buy a townhouse?

I'm 21 years of age, I only make $45600, but I can save $38400 of that.

Just wondering if I were to buy a nice townhouse in a trendy area for $300 000 how much should I put as a down payment by the age of 23?

Thanks!
Added (1). I know it's impossible to pay off a mortgage unless you decide to live till you're 100 and work 24/7, but I would like the lowest mortgage payments possible.

Read more: How much should I save up to buy a townhouse?