Is drinking 4 units a day of beer unhealthy for male 23?

Too much. 2 drinks (beers) a day for men and 1 per day for women is considered moderate drinking. More than that is not recommended. Some now feel that moderate drinking is harmful longterm. Other factors affect this. If your drinking if a problem to anyone close to you, or affects you negatively then that is way too much then. See http://www.cdc.gov/alcohol/faqs.htm.