The iPad5 is a very old model of iPad. When compared with much more recent models, its capabilities are becoming more limited - and its limitations becoming progressively more obvious. While third-party Apps are likely to continue receiving benefit of App updates for a few years, many mainstream App Developers limit support to the current and immediately preceding major version or two.
As for how long Apple will continue to provide system software updates, contributors here cannot provide a definitive answer - as this information is known only to Apple. When mainstream support ceases, Apple typically only provide occasional “point” security updates. Core Apps, such as Safari, are unlikely to receive substantive feature updates.
With loss of full update support, your iPad5 will have entered its twilight period of update support. If used online - and especially if used to access financial or e-commerce Apps or services - you might be well advised to consider replacement with a more recent device within the next 12 months or so - in so doing benefiting from both enhanced functionality, regular security updates and full update support.
Be aware Banks and many financial institutions - and some e-commerce sites - are will likely mandate use of a browser version in receipt of security updates.