Yep, totally normal John.
Your body will build up a tolerance to certain parts of your training, ukemi, atemi's (partner dependant
) and stretches.
Although there are some techniques that will always be delightfully painful. Yonkyo being the main one, and nikkyo being the main two that hurt the most.
Your gonna love it bud.
N.B, eating the right things makes all the difference to training, hard or light. You will probably wont see a dramatic increase in your fitness with Aikido practice, unless your Sensei does conditioning training, however you will be much healthier with the right diet and regular exercise.