I have like 25 year old characters to begin with. After killing Rauerbitters for money, a year or two has passed,
but my characters have lost end and str and more. These characters are only at most 28 years old and yet their
stats have dropped like 9 points. Am I doing something wrong. Please advise.

There are bugs in the game that can make you lose stat points, i.e. if you buff yourself with multiple saints (at least some) and the buffs run out, they are not removed properly. Instead of reverting to your original stats the reversal goes further and your stats are lowered. IIRC as an example, if you buff yourselves with multiple Raymond Penafort prayers, your int after the prayers run out will actually be lower than what it was originally.

Also there are some encounters that can lower your stats but they are very rare and IIRC in the amount of 1-2 points. So if the stat loss is more severe it's most likely due to bugs. The best really is to make a print screen of your original stats and if your stats are lowered, fix it with a char editor.

Also, aging ingame doesn't lower your stats. Only aging in chargen lowers your stats. That said, your characters can die of old age I think at the age of 90. In the old yahoo groups, there was a user that was exploring this. I don't remember the exact age, but it's definitely 60+.

So just revert your stats with a char editor.