Betta Fish: is this fin rot or is he just changing/growing? 😞🤞

hello, it’s my first time posting here and i just wanted some guidance with my betta. his name astro! ⭐️ we’re from the philippines.

i have pictures below of his fins from a few days after i got him, to what they look like now. he is actively eating and interacting, not lethargic, and his fins doesn’t seem to have any white or dark spots.

i also searched that he could be a combtail/crowntail mix if i am not mistaken. i’ve seen pictures of them that look like him now, but i am also not sure and i’m worried that it could really be fin rot or maybe he’s just changing/growing :’) i love him very much and would appreciate any kind answers! thank you 🙂