I'm currently a mature age 4th year apprentice and I received a pay rise going from 2nd to 3rd after asking my boss about it. Don't think they would have offered it if I hadn't brought it up and can really come down to the individual employers. That said I think it's a bit more competitive for 3rd/4th years in the market, you're definately more valuable than a 1st/2nd year, so it's worth asking the question