IMO as long as he keeps feeding, there isnt a problem with breeding a small male. I paired my pastel butter when he was 350ish grams and this was the result



The pastel butter kept growing and is now sitting at a little over 800g. Now, you do have to be careful breeding smaller males. My rule is they only get to see their girl if they are eating, they start a food strike and I pull them. There is also the chance that even if he is producing plugs he wont breed. Even though my pastel butter male started young, my pewter waited until he hit 700g to give the ladies a second look