i would say a long as the sling feels secure and you are comfy, then it will be fine. All slings should be weight tested, but depending on where you got it from, you might not know to what weight. I would give it a go, and see how you, and Alfie feel :)
For security, you are probably bet off with a mei tai, but for ease of popping him in and out if he has a tendency to want to get up and down, a pouch/ring sling might be good.
HTH
Claire x