It’s not about being in your thirties. What you are experiencing is depression.
You’re rationalizing and justifying your depression by associating it with age and portraying it as an unavoidable rite of passage. I don’t say this to try and change the course of your life, I just think it’s worth addressing your demons by their real names. It makes everything a lot easier, even if you really do decide in the end not to fight them.
Just my 2c, wishing all the best to you