40 - 50 pull ups at the beginning of every workout?

Hey guys. Over the past year or so I've just developed the habit of starting each workout with about 4-5 sets of 10-15 reps of pull ups just to warm up and get my blood flowing. Pull ups are my favourite exercise and I just enjoy doing them.

However, a buddy of mine told me that I should stop doing pull ups every day as it could be limiting my potential gains. Is this true/possible? I don't really ever have trouble getting through the pull ups, even after a back day.

I'm 21, 6'0 165. I've been working out for about 3 years.

Thanks