Simple things

[Hitman]

Updated. 

For example tatoo, you can make one when you are 20 years and you will maybe regret when you are 40 years old.

Even now techniques to remove tattoos are pretty advanced, and i doubt its going to be any problem at all in 20 years.

imo you can do almost all things you can do with 20 with 40 just fine aswell, and why would you do things that your gonna regret in the first place?

If something is worth doing, you wont regret it, and if it isnt, you simply dont do it