When I feel that I'm old

While I'm still in the middle of my vacation and won't be back to work till beginning next year, I spend a lot of time with my baby son. Taking him to the park is almost the daily routine. Man, just playing with him, watching him with so much energy, I'm feeling old. What can I say? it is an undeniable feeling. Just can't help but the time that I spend with him just keep reminding me that.