You're describing me until about age 30. 1. You need to realize that if something was easy or obvious, it would already exist. The only things worth doing are things that appear impossible. 2. Don't try to keep it all in your head at once. Get good at making a plan or a list of steps, following them (almost blindly), and correcting course every few steps. Taking a big problem apart and bringing small steps to complet…
Where were you before you turned 30, what did you do that you did or did not like? And what happened to trigger the change in your thirtieth year?
One thing that helped me towards getting them done has been to make projects as small as possible. For anything that I can't do in an afternoon, I try to make sure I can accomplish something small every day.
But it also took a lot of practice at improving self discipline (reading about it, writing about it, building habits), fixing my sleep schedule (way less lazy when I go to sleep at 11pm and wake up at 7am), and starting on pills to combat depression.
As others have said, make sure you love what you're working on. That's important. Don't get sucked into our society's focus on "productivity" over all else if it's not what works for you. There's more to life than producing output, and you are not what you create.