My son has moved up to a 19" Trials and is selling his 16" Jugglebug purchased in July-08. It is in great shape and comes w/ a street tire and knobby tire. Asking $80 CDN Calgary, Canada
How old is he?
I’m just learning to ride myself and have two young sons…
He was seven when he started (last summer). He’s now eight. Young kids these days learn way too easily and quickly 
Our other son is ten and he’s pretty amazing on his!
My oldest will be 5 in a month. He can really rock out on his two wheeler (dirt trails etc) but maybe it’s too soon to take away one of his wheels!
Don’t under estimate him!
Our 4yo nephew did manage to make a few revs on the uni last summer. It really depends on how agile they are. It too our younger son two days to get going on his.
Our older son had this cheap uni my wife bought at a market in China (the frame wasn’t square, the wheel wasn’t round, etc) and he got it going in about 5 days. Then continued to ride it into the ground until it completely broke.
How tall is he? I can measure up the uni if you like.
PM me and we can take it from there.