When electric guitar strings get a bit old, do they fall out of tune easier?

My guitar use to hold it's tuning like a champ but recently my 3rd string (g) has been falling out of tune, not horrible but I have to re-tune after every couple songs. Before I could wail out basically a whole set without it falling too flat. Honestly, I haven't change the strings in a good 6 months. Just changed em today, do you think this will help them stay in tune, or is it a guitar issue?