This is very difficult to answer. The size of a Scottish wildcat is another thing that has been confused by hybridisation.

Most sources state that wildcats are up to 50% larger than a domestic cat. Given that domestic cats vary in size a great deal, this description is of limited value.

It adds further difficulty to the answer when you consider that these observations have been made by people observing hybrids which were mistaken as wildcats. These hybrids were observed in captivity, or were actually European wildcats.

how long they live :

Wildcats live until around 7 years of age in the wild, and up to 15 years old in captivity. 

Enemies :
Predators such as eagles and foxes are a threat to unguarded kittens but will avoid confrontations with adult cats.
In the wild, a wildcat may sustain injuries which prevent it from hunting.  Humans cause injury and death via shooting, snaring and road kills.  There are no reliable statistics on the most common causes of death.

When is the best time to see them?
You can see red squirrels all year round because they don’t hibernate. You may hear the scratching sound of a red squirrel’s claws in the branches before you see it – and it might chatter crossly or even stamp its feet if you surprise it.

Red squirrels are active in the daytime but, like us, don’t really like being out in bad weather. They also enjoy an afternoon nap, especially when it’s hot. From January into early spring watch for red squirrels racing through the trees and spiralling up and down the trunks. This is mating time and the males are chasing after the females.

Otters have their cubs in underground burrows, known as a ‘holt’. Excellent and lithe swimmers, the young are in the water by 10 weeks of age.

Classified as Near Threatened on the IUCN Red List. Listed under CITES Appendix 1, protected in the UK under the Wildlife and Countryside Act, 1981, and classified as a Priority Species in the UK Biodiversity Action Plan.

A rare but widespread animal, now found almost throughout the country, but absent from parts of central and southern England, the Isle of Man, the Isles of Scilly and the Channel Islands.

they can be seen the whole year.

Facts
Seeing the signs of otters is far easier than seeing the animals themselves. Along riverbanks and waterways, look for five-toed footprints (about 6-7cm long) and droppings or ‘spraints’. Otters leave spraints in prominent places, such as fallen trees, weirs and bridges, as ‘scented messages’, helping them to find mates and defend territories. They contain visible fish bones and have a distinctive, pleasant smell, reminiscent of Jasmine tea.