How old is the Pentecostal Holiness Church?

The age of Holiness Pentecostal church is undetermined. But, the first congregation of Pentecostals, was also the first congregation of Christians. In the Upper Room was the first sanctuary, where Jesus told his followers to tarry. So, It's been awhile. :]

How we figure they're Pentecostal is they follow the signs. As do all Pentecostal churches.

By the way: Pentecostal comes from the day of Pentecost. The day when the Holy Ghost came from Heaven.