Liev Schreiber and son Sasha
08/02/2009 AT 03:00 PM EDT
Since becoming a father, Liev Schreiber may have sprouted a few gray hairs on his head but the changes go beyond the external.
The 41-year-old actor says he has become more youthful as a result of sons Alexander (Sasha) Pete, 2, and Samuel Kai, 7 months.
"I feel much older," Schreiber told PEOPLE at the New York City premiere of his film Taking Woodstock
on Wednesday. "I'm older physically, but spiritually much younger."
The once intense and guarded star is enjoying family life with longtime fiancée Naomi Watts
, 40, and showing off his younger, carefree side as a result. Whether playing in the sand at the beach, swimming in a pool in Italy or carrying his sons high atop his shoulders on the streets of New York, Schreiber is clearly relishing fatherhood.
The payoff is becoming clear, as his older son is starting to talk – and is on the verge of saying those three important words that all parents love to hear.
"Sasha has learned how to say 'I love you,' " Schreiber shares. "It's unrecognizable but he does say it. Rhythmically he can kind of sound it out. It kind of sounds like 'Iwoveu,' which is very exciting."
opens nationwide in late August.