Could I write off my startup expenses this year even though I have not had any revenues from my startup companies?

If you understand U.S. Income Tax Laws, please kindly respond:

This year I incurred startup expenses for some companies
I am in the process of establishing. My questions are:

1) Could I write off my startup expenses this year
even though I have not had any revenues from my startup
companies? (I do have interest income this year from my bank
account) Could I wait until next year?

2) If not, could I write off these expenses when
I realize revenues from my startup companies?

Thank you kindly in advance for your answers!