Japan's aging population seems to have added to the number of biker gangs, as a police report shows that the percentage of gang members aged 20 or over has exceeded 50 percent for the first time.

The report issued by the National Police Agency also highlighted an increased trend of former biker gang members getting together to recklessly ride old-model motorcycles.

The agency said that last year 847 biker gangs were confirmed to exist across Japan, an 11.4 percent drop from the previous year. The total number of members also fell 9.3 percent from the previous year to hit 13,677 members, a record low. The ratio of people in the gangs aged 20 or over stood at 51.1 percent.

Altogether there were 619 gangs with fewer than 10 members. Another 218 gangs had between 10 and 29 members, and 10 gangs had between 30 and 49 members. There were no biker gangs confirmed to have 50 members or more, a trend continuing from the previous year.

The number of groups made up of former motorcycle gang members reached 428, an increase of 137 groups compared with the previous year. The groups had a combined total of about 4,000 members, and reckless riding was reported on 28 occasions, with some 3,600 vehicles involved.

Altogether, the biker gangs rode recklessly in groups on 4,730 occasions last year, a 3.5 percent increase compared to the year before. Police said smaller groups were more likely to ride recklessly.

The police report said that altogether there were 825 gangs whose main purpose was to ride recklessly, a drop of 112 gangs compared with the previous year. There were 22 groups that were formed to hold illegal races, including high-speed races on expressways.