She was relatively young for a Vulcan when ENT was on (mid 60s). Vulcans can live for up to 200 years, since Sarek was an old man by the TNG era. During this era T'Pol should be about 165 or so - basically middle aged. They might need to use some light aging makeup on her, but that's all.
For some reason I was thinking she'd be around the age that she was in the season 3 episode 'E2' with that second Enterprise that went 117 years into the past. She was 182 there and seemed pretty old a frail.