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Distorted and browned leaves are often a sign of small sucking insects, scale or aphids. Some of them are extremely difficult to see. The best thing for you to do would be to take some leaf samples to the local ExtensionService for analysis. This link will help you locate the closest one: https://www.gardeningknowhow.com/extension-search/

It's just the general practice to prune many evergreens, etc. in spring, when they've broken dormancy. However, you can prune it later if you want, just not so late that winter weather might damage new growth. You will also be cutting off your fall flowers, of course.

If you had a particularly harsh winter, your elaeagnus may have suffered a cold injury or, given that your bush is 20 years old, it could be old age and weariness. It could also be the work of an insect - the "vine weevil" is known to feast on elaeagnus shrubs.

For information on winter injury in shrubs and how to treat it, please visit the following link:
https://www.gardeningknowhow.com/ornamental/shrubs/shgen/winter-damage-of-shrubs.htm

For more information on weevils, go here:
https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-root-weevil.htm

For information on how to care for elaeagnus plants, please visit the following link:
https://www.gardeningknowhow.com/ornamental/shrubs/elaeagnus/russian-olive-information.htm

Elaeagnus varieties can be deciduous or evergreen depending on the climate. Perhaps the leaves are yellowing in preparation for winter (if you are in the northern hemisphere).

Here are some other general reasons a plant's leaves might turn yellow:
https://www.gardeningknowhow.com/plant-problems/environmental/plant-leaves-turn-yellow.htm

It would be wonderful if every plant or tree we every planted was successful, but sometimes that is not the case.
Starting with well cared for nursery stock helps and then mother nature plays a very large part.

Light, sandy soil is preferred for this shrub. Well draining soil is very important. Watering new planting is very important in the first few weeks and then you can generally taper off.

Most reputable garden centers offer a guarantee or replacement of plants that perish in the first year of planting.

Here is a link to refresh you on the care requirements.

https://www.gardeningknowhow.com/ornamental/shrubs/elaeagnus/russian-olive-information.htm

First, it is important to know that you will never have to give these foods high in nitrogen. They fix their own. It could be, however, that they need a little phosphorus and potassium. Feed them a little bit of fertilizer high in these. Also, to give it the energy it needs to flower, you should cut back any new extra growth such as shoots coming out of the ground from the roots. This will ensure it has the energy it needs to grow flowers instead of shoots. Here is some more information on the plant:

https://www.gardeningknowhow.com/ornamental/shrubs/elaeagnus/russian-olive-information.htm