Read the article date_age - Lasso 8 Custom Tag Returns Age in Years.
[date_age]
returns age in years. By default the current date is used to determine age, but can be overridden by passing in a second date.
Demo.
date_age(-dob=date('2000-02-29'));
'<br />';
date_age(-dob=date('2000-02-28'), -end=date('2010-03-01'));
=>
10
10
Instructions for installing date_age
are in the demo file date_age_demo/index.lasso
.