I only have one boy (5). But still I want to give u what I think about your worry.
I think it would be good to have a second child while your son is still young, so that they can play together and less age difference. If your husband sugguested that you guys should have a second one, that means he thinks that he is ready financially, physically and emotionally - to me it's a good news. I wish my husband would say this to me too. But he said to raise a child in HK is very expensive.
Thirty something is not really old. My friend has her 1st child when she was 34 and 2nd at 36. Both are well and healthy. So don't worry too much!