Lock Data In Cell After Entering Value?

0: i have a sheet 1 protected and few edit range (Col A,B,C,D,E and F).

1: I have a validation on multiple adjacent columns (like Col A, Col C, Col E).
2: I need a code where if i select value in col a (cell A2) cell B2 should get current date and Time and both the cells (A2 and B2) should be locked. when i select data in cell C2 , D2 should get current date and time(Cell C2 and D2 should be protected).
3: User can enter data in A3 and B3 will get current date and Time (now A3 and B3) should be locked.
4: I need a function where user can call it and unlock the locked cells and edit the data and re-lock the cells again.

apart from the Col A,B,C,D,E and F, other columns and cells remain locked.