The 20-year-old joined Salop in the summer on a season-long loan deal from his parent club Chelsea.
Since moving to Shropshire, the youngster has made 14 League One appearances - with 12 of those coming from the start - and he has scored twice.
And speaking in a recent interview with football.london, Castledine says he has already gained so much from the loan experience, which he described as a 'massive step up'.
"It has opened my eyes up to the Football League a lot and how different it can be," he said. "It's a massive step up and change to academy football, but I have tried to take it into my stride as much as I can.
“I think it’s been a really positive (experience), not for me personally or even as a team. We struggled at the start of the season, it was tough the first couple of games, and it didn’t go as planned, but I have always thought there was a foundation in the team.
"And with the right leadership and mentality going forward, I can’t see any problems.
“I think I have done alright. With it being my first loan, my main focus was to come here and do as well as I can, show who I am as a player as a personality, stay in the team as much as I can and help the team as much as I can as well.
"I was playing a lot of Premier League Two football back at Chelsea, and I think my time had come where I was ready to take the next step into men's football and coming here to a place like Shrewsbury has been good for me."
Part of the move has seen Castledine move away from his home in London to Shropshire, where lives on his own.
And he believes that is helping him become a man.
"I've lived in London for my whole life," he continued. "So this is my first time living away from home, but I'm really enjoying it. Shrewsbury is an amazing town, really nice people. I'm living by myself, and it's good for me. With it being my first loan, I think it's good to have that experience of doing my own things and becoming a man.
"I think as a team we are really pushing, we want to stay up and get as high as we can in the table, personally I think it's just to keep trying to play as many games as I can and helping the team as much as I can whether that’s scoring goals or getting assists or putting in good performances."
Castledine will be part of the Shrewsbury squad that makes the trip to Cambridge today as they seek to get back to winning ways after losing to Blackpool on Wednesday night.