You can look for a script on the internet and try to implement that. Or you can ask your question around that ("how can I implement this script in my site"). It's a lot less work to implement a script than make a new plugin.
http://stackoverflow.com/questions/15738...javascript
http://codecanyon.net/item/agelock-age-v...pt/4931493
http://jquerywall.com/demo-age-verificat...atepicker/
http://community.hostcheetah.com/thread/439
etc. etc. There are a lot of scripts on the net:
Google age validation script
Personally I find the Yes / No question better than asking to fill in a date.
http://stackoverflow.com/questions/15738...javascript
http://codecanyon.net/item/agelock-age-v...pt/4931493
http://jquerywall.com/demo-age-verificat...atepicker/
http://community.hostcheetah.com/thread/439
etc. etc. There are a lot of scripts on the net:
Google age validation script
Personally I find the Yes / No question better than asking to fill in a date.