Deny certain user from updating certain rows Say I have a table like this:

canModify | name | age 
------------------------
    1     | John | 24
    0     | Nick | 21


I want to grant update access to a specific user only where canModify=1

I know there is column level security, something like:

DENY UPDATE ON Table(column) TO user;


But I can't find anything like:

DENY UPDATE ON Table To user
WHERE Table.canModify = 1


Is there a trigger or something I can set up to do this?
In my opinion, if you are stuck with sql server 2012, the Row Level Security is not going to work for you.

So you have two options:
1) application layer, which was already mentioned.
2) on database level, an trigger may work