Foster has impressed for the Baggies this season, helping the club to eighth place, four points behind Liverpool.
And goalkeeping coach Kiely, who won promotion with Charlton at 30, insists Foster can grow with age.
"I still think Ben can get better and better," said Kiely.
"He was 30 yesterday and for me the years between 30 and 40 were my golden era. It's exciting times for both him and the football club.
"My golden era was at Charlton and it wasn't a coincidence my family was settled and I liked the club. I played my best football there for those reasons and I think Ben is in a similar situation.
"Everything seems to fit. It seems to suit. Ben is a joy to work with. I think he has improved us no end and people see that when he's playing.
"But I have to say in and around the changing room from Monday to Friday, he's a real good character and top professional. He's a top fella too which obviously comes into it."