His weight is within the normal range for his species.
Yet for reason of his age, if you aren't already including Pycnogenol in his diet, I would add it. . Pycnogenol (extract of the cambium layer of the Maritime pine) provides a surrogate source of the inner tree bark (the living layer) that contains a high polyphenol contents, that is the elixer of life for tree squirrels. Older squirrels that were given this source were reported to have more energy. In rat research, PYC also was found to improve the circulation of the blood vessels and the function of the heart. The dosage for these
Healthy Origins 30 mg. and divided the dose down to 1/8 portion (not tsp.) of the total powder in one capsule given daily in foods.
https://www.amazon.com/Healthy-Orgin...7&s=hpc&sr=1-4
Since rodents age the function of the kidneys lowers so that they progressively retain more and more phosphorus as a result. With the calcium and other nutrients lowering but more phosphorus even so lowered is retained, it changes the in body Ca:P ratio. If the block fed is already a close ratio under (2:1) what is supportive of juveniles, but not adult squirrels, it can put him at risk to developing kidneys stones. For this reason, raising the level of calcium in the diet, in particular with Calcium citrate, not Calcium carbonate, for the citrate form in rats was found to improve and extend lifetime kidney function, yet the C. carbonate for not, as the latter form promotes urinary calculi (calcium crystals) to form n the urine.
By increasing calcium in the diet by adding a bit more calcium in the form of Calcium citrate powder (NOW Brand with no additives available on Amazon.com), can improve kidney function which can lengthen the life function of the kidneys. Adding the Calcium citrate to yogurt is a plus plus, for it has a positive Ca;P ratio, and is a higher calcium source.
NOW Brand carries pure C. citrate powder with no additives.
https://www.amazon.com/NOW-Foods-Cal.../dp/B0006ZF9NC
Stonyfield plain organic creamy yogurt is one that has been well vetted in my research diet. Adding a tiny measure of wild grown blueberries whole berry powder to the yogurt (check with me by PM for the measure), that is high in anti oxidants, and also higher in calcium than phosphorus than cultivated blueberries are, is advisable as it helps to inhibit UTI. This is especially important when feeding raw greens to lend support for the mean urine pH. to fall within the mid 6 range. Testing his urine with Urine testing strips is advisable, for if above 7.0, or below 6.0, you can then adjust the diet to better support an optimum healthy mean urine pH that falls in the mid to high 6 range for mean urine pH.
Mission Brand is one that is more comprehensive, yet laboratory rat paper brand will work to determine mean urine pH.
https://www.amazon.com/Urine-Strips-...0133643&sr=8-2
https://www.amazon.com/Litmus-Strips...0133607&sr=8-3
https://www.amazon.com/Blueberry-Pow...1&s=hpc&sr=1-2
Will send the measure by PM should you desire to include this in your squirrel's diet.
The level of phosphorus in the whole diet, not just the amount of nuts included daily, should be lowered, for as rodents age their kidneys retain more and more phosphorus; this even so all nutrient absorption lowers over time. For this cause their actual Ca:P in body ratio lower, which is harder on the kidneys so that it reduces their function quicker.
http://www.2ndchance.info/ratkidney.htm
No more than (1/2) Tsp. of organic chopped nuts daily; hazelnuts (filberts) the go to nut for this species, 1 hazelnut is about the same measure as this measure. Lowering the amounts and frequency of other foods higher in (P:Ca) , like avocado, is also needful; for though very healthy, this source is very high in ratio of phosphorus to calcium. Meal worms are also a healthy source, yet like avocado very high in P:Ca ratio. Feeding no more than one of these higher phosphorus sources when feeding a block diet, should be limited to no more than (1/4 Tsp.) level measure, and no more than a couple times a week when fed.