Can a 0.05% tretinoine cream help the red marks, caused by old acne, present on my face + some mild scars? If no, what do I use instead? If yes, time?

Won't work. The red marks will fade only with time. The scars can be managed only by a dermatologist or plastic surgeon. Manage your disease if still active and I am sorry you were not treated scientifically when you should have been. These marks matter little if you're otherwise living and presenting yourself well. Good luck.