I can't really find any official/canonical/whatever-it's-called sources, but this random youtube video at 0:49 says he was "in his 50s", and page 64 of the the book Modern Masters Volume 3: Bruce Timm says he was 80:

Bruce Wayne at age 80, as he appeared in Batman Beyond.

 

(1 , 2)

(also 80s looks way more likely to me than 50s, but I'm no expert)

I can't really find any official/canonical/whatever-it's-called sources, but this random youtube video at 0:49 says he was "in his 50s", and page 64 of the the book Modern Masters Volume 3: Bruce Timm says he was 80:

Bruce Wayne at age 80, as he appeared in Batman Beyond.

(1 , 2)

(also 80s looks way more likely to me than 50s, but I'm no expert)

i can't really find any official/canoncial/whatever-it's-called sources, but this random youtube video at 0:49 says he was "in his 50s", and page 64 of the the book Modern Masters Volume 3: Bruce Timm says he was 80, quote

Bruce Wayne at age 80, as he appeared in Batman Beyond

(1 , 2)

(also 80s looks way more likely to me than 50's, but i'm no expert)

I can't really find any official/canonical/whatever-it's-called sources, but this random youtube video at 0:49 says he was "in his 50s", and page 64 of the the book Modern Masters Volume 3: Bruce Timm says he was 80:

Bruce Wayne at age 80, as he appeared in Batman Beyond.

(1 , 2)

(also 80s looks way more likely to me than 50s, but I'm no expert)