Vim: Calculating age in substitution

Let's say you have:
source: https://sanctum.geek.nz/arabesque/advanced-vim-macros/

    Stallman   Richard   GNU    1953  USA
    Wall       Larry     Perl   1954  USA
    Moolenar   Bram      Vim    1961  Netherlands
    Tridgell   Andrew    Samba  1967  Australia
    Matsumoto  Yukihiro  Ruby   1965  Japan
    Ritchie    Dennis    C      1941  USA
    Thompson   Ken       Unix   1943  USA

and you want to calculate how old each of these guys above
is right now:

My solution with no macros:

    :%s,\d\+,\=strftime("%Y")-submatch(0)

    Stallman   Richard   GNU    66  USA
    Wall       Larry     Perl   65  USA
    Moolenar   Bram      Vim    58  Netherlands
    Tridgell   Andrew    Samba  52  Australia
    Matsumoto  Yukihiro  Ruby   54  Japan
    Ritchie    Dennis    C      78  USA
    Thompson   Ken       Unix   76  USA

Tip 1: Use Regular Expressions to match the numbers

\d\+ means: find a digit or more. That regex matches exactly our fourth column

Tip 2: Exchange Delimiter

In my case typing comma is much easier than typing slash, so I have exchanged the substitution delimiter.

Tip 3: Not always we need the global substitution

In our case we just need the substitution once, so we omitted the final coma plus 'g'

Tip 4: Use expression register in substitution

In order to use expression register in substitution just type \=

Tip 5: To get current year

We are using strftime("%Y")

Tip 6: Submatch(0)

It matches the pattern we just referred on the search part of the substitution

For more information use the vim help system:
:h regex
:h \=
:h submatch
:h strftime