I get 30 mph out of mine it has a decent motor on the bike, it has been I think purposely designed to four-stroke at about 20 - 25 to protect the children who ride them. However if you are like my self and own one and want to increase top speed try removing the air box and applying some tape (preferably metal tape) over the hole to the air cleaner, only cover the hole halfway, you may be surprised the increase in top end, if you don't believe this run the bike on the stand first at wide open throttle and put your finger over the hole partially obstructing air flow until you hear the rpm shoot up that's the amount up obstruction you want to use with tape, I got almost 10 mph more out of this bike and I have tried almost everything else recommended on these forums.
Could hurt to try
good luck