I've heard that... in some story lines, he's nearly 50 years old by the time he quits. I have yet to see anything on panel proving/disproving this however.

In the DCEU, he's roughly 44 in justice league.

What about the comics? is there any info available on this?

55 probably.

Depends on the health issues. DCAU Batman retired because of heart attack on patrol.

Realistically about 30

45-50

Around 60!