Last year I purchased a plum tree from the local grocery store, no leaves on it at the time. Planted it in black clay laden soil. 1 year later I have a tree that went from 5.5 ft to 6.5 ft., didn't prune the bottom at all. I have 11 plums this year (1st year not second). One plum turned color already and dropped, the other 10 still green and growing in size.
Question: Is it normal for a early color change on one fruit?

Also I have limbs all the way to the ground on the trunk, when should these be eliminated?
Thanks in advance