Age is not a complete problem statement
A system can use older technology while serving its main workflows well, or have a modern appearance while being difficult to change. Before choosing a rewrite, name the actual constraints: one slow area, integration difficulty, missing tests, expensive changes or dependence on one person’s knowledge. Each problem may need a different response.
Find the knowledge hidden in the system
Older software often contains rules that are absent from documentation but understood through daily use. Rewriting without discovering them can remove important behaviour unintentionally. Data analysis, user interviews and recorded real-world scenarios are part of migration, not secondary tasks to postpone until the replacement has been built.
Choose a separable part
Where a component has clear data and responsibility boundaries, staged change allows earlier evaluation and limits exposure. Define the connection between old and new versions, the data-transfer approach and a rollback point. Running both systems without data-ownership rules can create a new problem of its own.
Apply criteria to rewriting too
Structural limitations or the cost of continued maintenance can justify a rewrite. Even then, delivery should be staged and accompanied by data reconciliation and acceptance scenarios. A useful decision balances change cost, disruption risk and business value instead of treating newer technology as the objective.