Tips for managing a partner who may have anger issues?

My partner is 21 and I’m 26. We’ve been together for a year, and I’m uncertain whether his behavior is a permanent state or just part of his personal development, especially considering this is his first serious relationship and his frontal cortex is still maturing. He genuinely wants the best for me, takes responsibility for his actions, and often expresses gratitude for my patience with him. However, every few weeks, he experiences anger that he doesn’t always manage well. Over the course of our relationship, I've seen some improvement; he's stopped certain behaviors that he used to exhibit regularly. Still, he often gets upset, raises his voice, makes a few hurtful comments, and occasionally slams a door or an object during heated discussions. There’s one concerning trend: in the past, I could appeal to his logical side during his angry moments, and he’d quickly calm down. Lately, however, for the past couple of months, he seems to hold onto his anger longer, even when I get emotional, which used to trigger his empathy. Typically, after cooling down for about 30 minutes, he returns to apologize and appears genuinely remorseful, making an effort to treat me well for a while until the next trigger arises. When I address his reactions, he seems genuinely worried about how he behaves and admits he struggles to control it. I’ve seen him try to manage his anger, and it does seem challenging for him. I can’t fully relate to this struggle, which leaves me feeling confused. I can't help but wonder if he will always react this way. He tries to remain positive and hopeful that things will improve. I know that a few months ago, he confided in a friend about his outbursts and expressed worry about his behavior. He has been waiting for the new year to seek therapy and has started researching personal development and listening to podcasts about anger and self-control. While I can’t fully understand his lack of impulse control, I’ve recognized moments over the past couple of years where I’ve reacted differently than I might have at 20, surprising myself with my own growth. This gives me hope that he can change too, especially since he genuinely wants to improve and treat me better during conflicts. Is it common for people to struggle with how they treat their loved ones? Can it be resolved? Could his challenges be linked to his developing frontal cortex?