Does the size of your lips change as you grow older?

Yes. Lips will tend to lengthen and get thinner with age. Just one more of the wonderful benefits of getting older.
Yes. Lip thickness will typically decrease some and lips will lengthen with advancing age.
Yes. As the face passes through maturity of the skeletal & soft tissues, the lips will assume their full size and fullness. If front teeth are moved too far back orthodontically, the lips will as we orthos call it, "dish in". Through middle age & beyond, lessening of tissue fluid and particularly elasticity, lips thin and wrinkling occurs with the musculature of the face. Old age= thinner/receded lips.