If he's understanding well then you probably don't need to be overly concerned, but it might be worth reaching out to your health visitor so that he's on their radar in case you do need more support later on. I could be wrong, but I think the threshold for them to put support in place is if a child doesn't say 50 words by the time they're 2. In toddler time, that's a long way off yet, and lots could change in that time. I find that speech doesn't develop in a linear fashion - my little one will suddenly have a spurt and make a lot of progress in a short space of time.
My sons nursery are concerned as he dosnt say much. They will be doing a welcomm assesment hopefully this week to see where he is at with his speach and understanding. I think his understanding is great and he can communicate what he wants etc aswell but he just can't use many words right now. Perhaps reach out to your health Visitor and see what they think x
Boys tend to be very slow if he’s understanding I wouldn’t worry until he’s 2.5 xxx