At rest with no stimulants, stress, past medical history... and at you age- above 100 bpm (sustained for longer than 10 minutes) is cause for concern. If there are other symptoms (dizzy, loss of balance, blurred vision) then there is more reason for concern. At least call somewhere (ER, MD) for help.
It depends, I know the high hundreds is cause for serious concern because my heart rate went up to 200 and the paramedic warned me I could have a heart attack. If it's over 100 at rest it's something to look at (yes even between the ages of 21-30).
Would it be the same for someome that is like 21-30 years old?
Yup, pretty much the same...
