You should have received two Form 1099-R's for the pension income in the year you turn 59 1/2.
One with a code of 2 in box 7 for when you were under age 59 1/2 and one with a code of 7 in box 7 when you were age 59 1/2 and older.
Contact your plan administrator and find out why you did not receive the correctly coded Form 1099-R.
Probably they should have issued two 1099-R's with a code 2 for after 59 1/2, but you can enter it anyway.
When it asks if "we can lower your tax bill", enter the amount received after age 59 1/2 in "Other" and it will be excluded on a form 5329.
I'm in the same situation but taking distributions from an IRA. Will I simply get two 1099R forms? One would be for distributions before I turned 59 1/2 and one for after.
Yes, that applies to an IRA as well. You should receive two 1099-R with different codes as explained by @DoninGA.