Is there anything inherently gnostic or New Age about prayer labyrinths?
The labyrinth fad is an interesting and relatively harmless example of Catholics, mostly women religious, in older congregations, who, after having rejected the traditional forms of piety with which they were raised, fix their attention on other forms while trying to maintain a sense of continuity with the past.
Really, the labyrinth is meant to be a mini-pilgrimage, undertaken with prayerful attention. There are examples that are not fads and have survived into the present, such as the annual pilgrimages to St. Patrick's Purgatory on Loch Derg in Donegal in Ireland. These, however, are penitential exercises and not at all mild meditations in a grassy labyrinth in a retreat house somewhere in the Midwest or on the East Coast of America.
The labyrinth form is very ancient and penitential in origin, even if those who promote it now are generally allergic to any emphasis on penance or on the need to make reparation for sin. So if you take up a labyrinth exercise thanks to the encouragement of some nice lady religious, keep in mind that your distant forebears took it up in a spirit of repentance and deep self-knowledge. If she is encouraging you along that path, then it is all good. Say the rosary while you walk the labyrinth and then you will be close to the original idea, such as it is lived out in places like Loch Derg.