If you want to see a ton of yellow leaves, check out my balcony grow. I'm the master at growing yellow leaves. For the most part, it's because I waited too long into the grow before adding nutes. I gave it a lot of bloom nutes, which didn't stop the leaves from yellowing.
More importantly, yes, it is time for you to use nutes. Have you been giving it nutes while it's been vegging? If so, what kind? If you've never used nutes before, then your plant is low on Nitrogen, among others. Bloom nutes are also low in N. I would suggest getting some bloom nutes, AND some fish emulsion. Start with the fish emulsion to get plenty of N into your plant. I would try that first, then switch to the bloom nutes.
Got pics?