What is it you want to know? If a soaker tub is what you want this looks perfect and I as 76 and have no issues getting in and out of my 19" tub and your son will grow quickly . The length is not going to change so maybe if you are concerned add something on the edge of the tub you have to make it 19" to see if your wife is okay with that. Since this is a reno maybe also think about adding a grab bar on one side near the end for down the road or to make it easier to access.

The tub I was looking at was 21" I was wondering if it was a nuisance for short people to get in and out of.

I'm barely 5'0" and I'm going to order the Underscore K-1136. I was able to sit in one, and the height (22") was fine for me. I take a bath everyday too, and being able to get in and out easily is top priority for me (that's why I'm not getting a free-standing tub).

Please note the water depth is only 15.5"

You might find the same size tub from Maxx with deeper water and less expensive.