4.5 billion years is indeed much older than 10,000 yrs, jack, and assuming all possible factors are factored in ,we must take it as a reliable sum.
however, I am unsure of whether you are saying the sun began then and grew, or was then already near its present size and diminishing since.
I believe it is accepted that its core is diminishing as the burning process progresses over time.
what I would wonder is ,whether the calculations prove anything , when the creation model is of a fully formed and functioning sun operating from day 4 appr 6,000 or so yr ago.
there are also more technical answers which I am not feeling adequate to convey accurately. you might like to look up , the faint sun paradox, which discussion points rather to the sun being a problem for evolutionists more than creation believers