Brief Explanation of the Timeline
Let's briefly go over the timeline.
In the original novel, it's stated that Dugu Bo breaks through to become a Title Douluo at the age of 70. When he meets Tang San, he is 78 years old, and Tang San is already 13. That means Dugu Bo is 65 years older than Tang San.
Now, let's look at several major events in Douluo Continent:
1. Spirit Hunting Operation
At this time, Tang San is about 18 years old.
So Dugu Bo should be around 83 years old.
2. Heaven Dou Palace Coup
At this point, Tang San is already 20 years old.
That means Dugu Bo is about 85.
As far as I remember, these two events happen relatively close to each other, so this timeline should be correct.
Final: Battle of Jialing Pass
By this time, Tang San has already become a god, which puts him at around 25 years old.
At this point, Dugu Bo is exactly 90 years old.
All future settings will follow this timeline.
If anyone knows a more detailed or accurate timeline, feel free to leave a comment below. I'll make corrections where possible.