Mine is coming up 9 months and I have already done him although probably not gone as brutal as I could.
Are you perhaps trying to grab too much at once? I found if I grab too much it doesn't come but if I slide my finger under a fine bit of top coat it comes out very easily. I got on easy practice on his hind quarters tbh as he is black and the the coarse top layer there was brown.
I didn't get much out per tug but you can go very quickly when you start and I got a football sized ball of hair in around an hour. It did make my fingers sore though and someone on here suggested chalk powder for that.
I am going to invest in a stripping comb soon but quite enjoyed doing it by hand but then I am a self confessed hair picker
Our BT is 18 months old and we have n't stripped him yet, he is looking very scruffy but when we pull hair (gently!) it does nt come out some obviously not ready how old are they usually when have first strip