Any idea on its weight? Does it look skinny, fat, or in between?
How about the sex?
At 5 years old and 10' I'd guess it's a male, considering it's been fed well. In which case, it may not grow at all or maybe a foot tops.
If it's a 5 year old 10' female that has not been fed well, she will grow slowly to maybe another 4-5 feet considering you feed her well.