For my kids' 14th birthdays, we would get them their "adult" bike (~$400-500 entry level bike shop bike) that they shouldn't outgrow anymore. I have a daughter that is completely blind and we have done biking with tag-alongs and similar things, but it normally worked REALLY bad. Her balance as she grew older was terrible and normally made it frustrating to counterbalance her while pulling her. But we had the opportunity to try a tandem bike and to my surprise it worked really well. There are a few times I have to overcompensate, but since the bike doesn't have any pivot points, it is much easier to manage than the tag-along that pivoted on my bike seat. So for her 14th birthday, we bought a Schwinn Twinn and took it out. I'll probably tweak the bike a bit (upgrade the tires mainly), but overall a very nice and lower cost ($700) tandem bike. It needs some shifting adjustments, but otherwise worked well right out of the box from Amazon. She loves to bike, but our old setup just caused frustration. Hopefully with this setup, we can get a regular riding rhythm now.