Have a Session 0, or at least a real conversation about your expectations
This comes down to your social contract in the game and to expectations. The bottom line solution is to explain how the game works at your table and what kinds of input you would find helpful and what kinds you find to be unhelpful.
You don't need to take the reignsreins back...
Personally, as long as the players understood that they were making suggestions that I could accept or reject, I would welcome this kind of participation at my table. I go out of my way to work the character's backstory into the game and I encourage them to make it easy for me. So long as its clear that their suggestions are only suggestions, I personally do encourage this type of behavior.
Some RPGs encourage this type of thing by their very rules, especially those that use or are inspired by the FATE system. DNDD&D does not encourage this quite so much by its rules (though it does to a small degree), but it accepts it reasonably well and it is a valid play style.
...but you might want to take the reignsreins back, and the players should respect that.
However, I am well aware that not all DM'sDMs encourage that for a wide variety of reasons including wanting to develop the world themselves, wanting to move forward with tightly scripted plots, or simply wanting to focus on the combat. That is a valid playstyleplay style too. Most players, at least those I have dealt with, will be fine limiting their input on the world outside their characters, but it may need to be explicit. This is especially true when the players have a background at tables that encouraged that sort of input.
In short, taking the reignsreins back is probably as simple as telling your players that you want to. As long as you phrase it as identifying your style, rather than something like telling them their input was inherently bad, they will most likely not find it rude and will likely respect your position.