I have no idea whether or not he might get more orange specifically, but I do believe the patch on the chest gets larger with age. I've seen the pictures you've posted of him, and he is beautiful.
Roni is an orange vested. Her orange was as bright the first day I saw her as it is today, but she is only a few months older than Kiwi. I've been told her chest patch will get larger as she ages. I think some males may eventually have even larger patches than females.
Funny, though, she is an orange vested, but the color is more yellow on her legs than on her chest. That seems to be the opposite of Kiwi.
One other thing, I was back in the bird store yesterday visiting my son's new linnie, and I took a look at the baby senegals. They are all orange vested, but the very young babies DO have much smaller chest patches than Roni does. I did not see Roni or her clutchmate when they were unweaned. The store has one who is now about the age Roni was when I first saw her, and he is very bright orange and has about the same amount she does, maybe a bit less. The babies who are just feathering out have smaller patches, though. I just hadn't noticed until you asked the question.
There are several sub-species of senegal, though.
Did you see Kiwi's parents? How much yellow or orange did they have?
How old is your senegal? My senegal was yellow vested when I bought her, but after her first molt she looks like an orange vested! I think she was around 4-5 months old when her color changed. I'll have to upload the photos to show the difference. I don't know if this is a common occurance or not, but I know from experience its possible.