Can’t seem to get starter to double in 4-5 hours

My starter is about 2 months old. I’ve baked with it a few times with mediocre results. One thing I can’t see to do is get it so double in 4-5 hours. It usually takes 8-12.

On the days I want to bake with it I do a 1:1:1 ratio and use a mix of AP flour and whole wheat.

Lately I’ve been keeping it in the fridge for a few days at a time and then taking it out a day before using to wake it back up again. When it goes in the fridge it gets a 1:3:3 feeding.

Even before I was storing it in the fridge I still couldn’t get it to double in 4-5 hours. I’ve tried putting it in my oven with a pot of boiling water since my house is usually around 68-70 degrees and that helps some but still usually takes 7-8 hours.

Thoughts and advice?