Fix WordPress Plugin Issue on Old PHP

My WordPress site is experiencing issues with a problematic plugin and is currently running on an outdated PHP version. The site crashes on load, and while I have checked for plugin updates, I have not applied any.

I need an experienced WordPress developer who can:
- Resolve the malfunctioning plugin
- Fix the site crashing on load
- Work with the current old PHP version

Ideal Skills and Experience:
- Strong WordPress expertise
- Experience with PHP version compatibility issues
- Proven track record in troubleshooting plugins
- Knowledge of site performance optimization

Please provide a detailed plan and timeframe for the resolution.