No 'about', I think.I have understood about the tense
Note, from ... to are correlative, paired, set for life, and for that very reason, from is often omitted because we know it's always there. As for ranging in ages, it's a set phrase--for life, which is why ranging in can be omitted.
If Tom explained something to Peter, and finally Peter understood. Peter could say, " I got it."
But I never hear about other people say, 'I have gotten it.' in such a dialogue. So why did you use 'I have understood' here?
Could you please give me a hand again? Thank you!